Idle prob just won't go away! - Page 3

84porsche9113.2 · 06-19-2007, 06:02 PM

rcaradimos, thanks for the advice. I will try blowing air through the passageway with a compressor tonight as ned suggested and also use a stiff wire and carb cleaner to clean the passage.

On the other hand I did mention previously that I cleaned that area up really good. If the passageway is big enough for a qtip to fit in, I would have cleaned it already though. 1/8 sounds pretty small, so maybe not. Anyway, I'll double check again to be sure, but i thought i remember seeing the passageway going south (when looking in from the top of the TB) and I thought I had cleaned it up.

I also thought I may have air leakage at the idle set screw. the o ring looks okay but to be sure i put some dow 111 silicone on it to try to help seal the air out. That in and of itself did not help things.

Will try cleaning the passage again tonight and post the results later....

rcaradimos · 06-19-2007, 06:37 PM

84 north from screw/south from top plate = same.
Take the boot off spray from top w/ screw out and you should see cleaner flow in screw hole. This allows air to be drawn above throttle plate and may be reconized better by AFM barn door.
best of luck

Ned nyna 11 · 06-19-2007, 06:47 PM

On Carreras the design idle speed is 850. This is set using the bypass screw on the throttle body while the ICV is jumpered out. When you get the speed where you want it, The ICV is reconnected and the DME then continuously adjusts the ICV bypass to maintain the design speed, 850 in my '87.

What you want then is the ICV to be holding the speed at what it was set, for example when the A/C kicks in and the idle drops, the ICV will open to keep the set speed and prevent a stall.

So there is something wrong when you cannot adjust the idle with the bypass screw.

My opinion is that it is not passing air.

Steve W · Steve W's Garage

Check and try setting the base idle mixture to factory specs. Mixture has a big effect on idle speed, and is a key parameter in good idle. As this is a ROW car, it has no O2 sensor to sense and adjust the mixture. Around the correct mixture, generally as the mixture leans, the idle drops, and vice versa. Find someone with access a CO machine and set the CO to 1.0-1.5% at normal running temperature. Then fine tune the base idle speed jumpering the test jack at b-c to 800-880 rpm. If you still have the stock fuel pressure regulator, I'd suggest putting it back on to eliminate a variable. 3.2s don't need additional fuel pressure as the injectors can supply all the fuel the motor needs.

84porsche9113.2 · 06-19-2007, 06:59 PM

Ned, thanks for the info. That makes a lot of sense and was very enlightening as to how the ICV works in conjunction with the idle control screw...

Well the screw does look pretty long. I do like your explanation that the idle screw is not passing air, however, what puzzles me is why would the idle be strong upon start up and when the engine is at normal operating temps, but only be low in between??

From the way you describe how things work, it is almost as if the bypass orifice is openning up to let air through when engine is at normal operating temps, but constricting/not passing air when warm after startup to cause a rough low idle. But this does not seem to be physically possible! So I'm wondering if it is indeed something else (especially since I've already cleaned out the orifice).

As I said I will check the orifice again tonight, although I'm pretty sure I've cleaned it thoroughly already. If I still have the same problem after checking the orifice is clear, I guess things will have to progress to the next level of troubleshooting...

84porsche9113.2 · 06-19-2007, 07:07 PM

Thanks for the info Steve. I wouldn't mind buying a CO meter if it was cheap enough. Do they have handheld ones - what is the price range?

The only problem is it might be a while till I get my CO checked. I'd probably just have to hire a mechanic to check the CO and adjust the AFM...

I was really hoping it was a simple fix which I could solve without actually having to take it to a wrench (making appointments to pick up and drop off the car, etc. is such a hassle for me...)

Steve, is there any explanation why it appears I have the correct idle mixture (good idle) when engine is at normal temps but not when only slightly warm? You're saying the mixture might be leaning and idle dropping when the engine is warm after start up. So what then would be a possible explanation why the startup idle is good as well as why the idle at normal operating temperatures is good as well? If the A/F mixture was screwed up wouldn't it idle badly even at normal operating temps?

84porsche9113.2 · 06-19-2007, 07:09 PM

Snipernick - how do you guys adjust the mixture on CIS cars? Do you know? Maybe you should look into this as it seems that more than one post has mentioned that on 3.2's at least, setting the A/F mixture helps idle...

ninelevenick · 06-19-2007, 08:17 PM

Hey 84. Looks like you are getting some sound advice. This board is the best thing since fire and cooked meat! On my car A/F is set by turning a set screw (left=lean, right=rich I think) located near the fuel distributor. A gas analyzer is needed to accurately see the CO readings. I had this done about 1-1/2 ago and watched the mechanic do it. I haven't monkeyed with it since. Again, I didn't mean to high jack. I just thought that since my car has very similar symptoms, one could compare CIS and Motronic and use deductive reasoning to find a possible correlation and solution. However, since I have the podium, I will say that one time I was able to eliminate the warm-up idle problem by adjusting my WUR (tapping the pin) pretty far. It was a trade off though because during the first 30 sec. to 1 min. after startup, the car would idle hunt. This indicated a rich setting on the WUR. I have since purchased a CIS fuel pressure gauge and set the WUR to a point where I believe I have correct cold pressure. The startups are pretty good, but the trade-off is low idle between initial startup and warm op. temp. I know. I know; this does nothing to help your situation 84, but I couldn't help myself.

84porsche9113.2 · 09:11 PM

Snipernick, so when you adjusted the A/F ratio with the mechanic, did you still have the same problem we are both having? Did it or did it not solve the problem?

Actually I think what you are saying does help me to understand my situation. If my car is behaving the same as yours, in effect you're saying that when you set the WUR to rich, you had hunting idle but solved the warm-up idle problem. Additionally, SW (a very credible source) stated that a low idle is also generally indicative of a lean mixture...

So perhaps what is happening with both our cars is that the idle mixture is too lean during warm-up, but somehow, after the engine gets hot, the idle mixture gets richer to the point the idle rises....???

True, that does nothing to solve my specific problem but it does help to brainstorm at what possible causes might be and that in turn helps to better pinpoint where to look for the solution....

Rather than not enough air getting past the idle valve, could it be that too much air is going past it and causing a lean mixture (or maybe instead not enough fuel)??

Whatever the cause, it must be a condition that corrects (or goes away) when the engine gets to normal operatiing temperatures. So whatever is causing the mixture to be too lean (too much air, like a vacuum leak, or not enough fuel) is something that appears right after start up when warm, but goes away when the engine is hot....

For this reason, I find it hard to suspect the idle air valve orifice since I find it hard to explain how it could let air through when hot but not let air in when warming up (and also since I have already cleaned it). But again, I will blow air in there and double clean it again tonight just to be sure.... For the same reason, I'm also not so sure if it is the A/F mixture either (why would the idle condition correct only when hot if the a/f was indeed really off?), but I am willing to try anything as long as it has a high probability of working... If there were reasonable explanations to these questions, then I would definitely look into them much further...

Anyone else have any suggestions what to check assuming the cause of the condition is an abnormally lean mixture only upon warm up causing low idle, and that condition goes away and the mixture becomes correct & car idles properly when the engine gets to normal operating temps?

84porsche9113.2 · 11:26 PM

ned / rcaradimos,

checked the bypass orifice, clean as a whistle. you don't have to take my word for it, i'm attaching a pic for your assessment... now I do remember cleaning this out very thoroughly by removing the rubber boot several weeks ago to access the north/south tube (and by the way, the qtip did fit in there).... My idle problem was happening as recent as last night, so it apparently the low idle is not happening because air is not going past the idle screw....

so now that the ICV, idle switch and bypass screw/orifice seems to be ruled out, where could I go from here?

would a vacuum leak letting in unmetered air cause a rough/low idle just the same as a blocked bypass passage? could such a leak resolve itself if the engine gets hot? if not, what else might it be??

I am not going to be able to check CO as steve suggested for a while since I don't have the tools so if it could possibly be something else I wouldn't mind investingating any other possible leads while I'm waiting to take it in...

malpaslane · 06-20-2007, 12:38 AM

Hi all, just to drop this one in for the cis cars , i had really bad idle problems with my car , tried everything i could, played with mixture, changed all inlet gaskets and sealed everything i could find,only to find that my mixture adjusting screw wasn,t turning as it should,cleaned screw ,got it moving freely and now car runs and idles better than it ever has . i have heard that the cis mixture does go out of spec, so needs to be checked at regular intervals. hope this helps someone. Rik

84porsche9113.2 · 12:47 AM

I found this doing an internet search and it came up on a rennlist page. the page itself is about "D-Jetronic idle stability", which I don't know what that is (apparently it is for 914's). But seems like some of the things it says are applicable across the board..

*****************

My idle doesn't change when I open the air bleed screw. What's wrong?

Very lean idle mixture: When the mixture is very lean, the air bypass has no effect on the idle speed. Go to a shop and have your idle CO measured and set to spec on a shop-quality analyzer.

**************

Seems like this may be happening with my car. Looks like SW may be right. I guess I'll have to wait until I can take the car in to a shop and have the CO measured and AF adjusted....

Malpaslane, conincidentally you posted about a/f mixture too right before I posted this. So it seems where this is the concensus is headed.

However, I'm still not quite clear why if the mixture was lean when warming up, why it would richen up and the idle would get normal when the car is at normal operating temps... Anyone have any idea as to what could be causing this if the A/F mixture was indeed off (why does it correct itself when the engine gets to normal operating temps)??

SW, I'm curious, can I just play with the AFM adjustment screw to see how it changes idle and go based on that to get a rough idea (as it seems malpaslane has done - although he has a different system)? I saw another post said you can really screw it up doing this w/o the CO meter. I know it's best to do it with a shop that has the right equipment, but at least if I play with things and I can improve it or "get it in the ballpark" by feel alone (as to how it affects or increases idle), maybe I can fine tune it at the shop later.. Would this be advisable, if one was planning to eventually take it in, but one still wanted to experiment with the A/F ratio & adjustment screw w/o the CO meter in the meantime??

84porsche9113.2 · 06-20-2007, 01:27 AM

The factory manual states turning the mixture screw clockwise = richer mixture. Since I'm assuming my mixture is lean, what if I do what Ned said, block of the ICV, and when the idle is running low at 250 rpms, I adjust the mixture screw clockwise slightly until the idle comes up and the idle screw has more of an effect?? I know it would be basically doing it blind w/o the CO meter, but probably better than leaving the mixture as is (which is probably excessively lean), no?

Also, would anyone know where I would get the replacement plug for the mixture screw or can it be substituted with some other readily available item?? I read on another thread you can use an allen wrench? (factory manual says use special tool to the contrary). Anyone know what size allen wrench?

Steve W · Steve W's Garage

The mixture is variably adjusted through several sensors to keep idle within a particular range. On cold starts, the mixture is automatically richer because of the reduced fuel atomization due to a cold motor and port walls that would reduce idle speed. However as the engine goes through warmup, the head temp sensor tells the DME to start leaning the fuel mixture until the car is at normal running temp, when atomization is good and idle will be smooth. On cold starts, idle is typically higher for a minute or so because the cold sensors tell the DME to advance the idle ignition timing and the base idle speed of the ICV for the first minute or so to keep the car from stalling, but shortly thereafter starts dropping down to normal as the car warms. It is possible that your idle mixture is just lean enough to keep the idle below the window of adjustment of the idle control valve, so that when the motor is warming up, you are below the this window and experience the low idle problem. You can attempt to richen the mixture yourself with a 3mm hex wrench, but without an air fuel ratio meter or CO machine, you are just guessing. Try two full turns clockwise and note the result. Count your total turns so you can revert back if necessary. A poor man's mixture meter is to install a O2 sensor in the exhaust and measure the voltage coming off the sensor at idle and normal running temp. Properly adjusted, the voltage should swing evenly between 0.2 and 0.7 volts.

DonMo · DonMo's Garage

84, to find vaccum leaks, take a can of fuel injector cleaner and spray around the intake header and if the idle rises, you have a leak. Do the sme around the black boot, and afm (not around the opening). If you want to see what it will sound like with a leak, spray a little in the opening. Idle will increase with the additional fuel, then go down. Another easy problem to eliminate is to remove your AFM and clean it. They are notorious for having a lot of oily film build up and sometimes the buildup can keep the barn door from closing, in other words a big vaccum leak. Good luck. You got the right help now. Steve W. knows the inputs to the Motronics and fuel injection.

84porsche9113.2 · 06:50 AM

Steve -- that explanation was simply amazing! I have no doubt that every word you just said is absolutely probably true. Which is why I do think I should have my A/F ratio adjusted.

I took it out tonight, and my AFM seems to be a mess. It is missing the plastic cover plate as well as the plug for the A/F screw. Seems like someone has toyed with it before (it wasn't me). Perhaps to pass emissions?? Does the factory sell the plastic cover seperately? Is it a big deal to run without it? If any one has an extra one to sell, let me know...

What about the missing adjustment screw plug? Is there any other purpose to the plug other than to prevent someone tampering with it? If I run without one is it deterimental?? I guess I would want to know if these 2 items (black plastic cover and adjustment plug) are critical to the AFM. I've been running without them all this time, and except for this low idle issue, I haven't had any other problems. My parts book lists a part number for the plug, but not for the black plastic cover...

While I have it out, I also plan to do the mod moving the wipers arms which I found on this board recently. As I already have an O2 sensor installed, it would not be that hard for me to tap into the wires to measure the voltage as described.

DonMo - I've tired using propane in a similar manner and not gotten much luck. Even when putting it direclty into the intake, idle does not increase much. I wonder if this is because my mixture (as SW described) could be overly lean to begin with? In general if you have an overly lean mixture would trying to troubleshoot using propane or injection cleaner be harder to make the engine rev higher?

This board is absolutely amazing! In a little over 24 hours it seems that I appear to have found the solution to a problem that has been bugging me probably ever since I bought this car.. I just never bothered to take it to a mechanic or look into it this deeply before. Thanks again to everyone for their input and replies. I will post conclusively after I've had a chance to play with and adjust the A/F screw as SW suggested....

84porsche9113.2 · 09:04 AM

UPDATE: I did the wiper adjustment procedure as well as adjusted the adjustment screw 2 full turns clockwise. Upon startup, although the idle still drops, when I block off the ICV out of the picture, it does seem that idle has improved.

BEFORE adjustment: With idle screw backed all the way out and ICV blocked off, car was running at 250 rpms when warm.

AFTER adjustment (2 full turns clockwise): With the idle screw backed all the way out and ICV blocked off, car is now running at 500 rpms when warm.

So, adjusting the AF ratio does in fact seem to be working...

Steve, what do you think? Should I go further and try turning the screw another 2 turns clockwise??

Also, about how many rpms should I be idling at with the ICV blocked off and the idle screw backed out all the way?? It seems from previous posts that I should at least be able to get 850, but my thinking is if the screw is backed out all the way, it should be higher than 850, right? So what is the max rpms one should be able to get with the idle screw backed out all the way??

Thanks in advance...

Ned nyna 11 · 06-20-2007, 07:35 AM

Always best to fix whats wrong before getting in any deeper.

Set the mixture with instruments and then we can carry on.

84porsche9113.2 · 06-20-2007, 08:59 AM

Ned,

Ok, well I won't have access to instruments for a while. So if you're willing to wait several months or more, I'll report back then... Thanks...

84porsche9113.2 · 12:14 PM

UPDATE - PROBLEM SOLVED: Just in case there may be other besides Ned who are interested to know what the final result was...

I ended up giving it another 3/4 turn so a total of 2 3/4 turn. At that point my O2 sensor readings were toggling my digital multimeter between 0 and 1. It would read 0, 1, 0, 1, 0, 1... etc.

I am guessing anything under .5 is a 0 and anything above is a 1.... So it would seem my mixture is now correct, according to the O2 readings anyway.

The low idle is no longer there but for some reason now my idle switch is acting up and I am periodically getting high idle by 500 rpms. I need to finish adjusting that and I think my idle will be as perfect as it is going to get without doing the actual CO test.

Unfortunately, the O2 readings are good enough evidence for me that the mixture is set correctly and I probalby won't be taking it in for CO... Sorry Ned. I think I really would have liked to take it in, but I think one of the points of this board is to help to try to save everyone some $$ mechanic's fees, and I think that would defeat the purpose to pay $$ when the car seems to run fine and the O2 readings appear to be accurate. If something was amiss or the car was running crappy, and I didn't know what else to do, I'd be forced to take it in. But luckily for me (and again thanks to everyone's input -- especially ned & SW), that is not the result here... (I might have still taken it in if things had been different and I was not able to verify with the O2 readings that things were set properly..)

All I can say is with the help of everyone (too many to name here..), I solved this very irritating problem. Hope this thread was of help to many others who may have similar problems as well. Again, thanks to everyone...