High idle when warm

jbrand540 · 03-08-2008, 01:02 PM

I recently installed a Steve Wong chip and now after the engine has warmed up it will idle in the 1200+ rpm range. Could this be the CHT sensor? It checks fine with a voltmeter, however, I have the older single CHT. I have read on issues before where high-idle was caused by a faulty CHT.

Before the car gets up to full operating temparuter it will idle just below 1000 and the idle is rock steady. I tried adjusting the idle to counter this and currently have the idle screw all the way in which has lowered the idle to just below 1000 rpm, however, once fully warm the idle will still shoot up to the 1200 range.

kach22i · kach22i's Garage

Do MFI owners do what CIS owners do to find leaks in the system (starting fluid method with extinguisher nearby)?

I have no idea, just giving you a bump I guess.

jimbauman · 03-08-2008, 06:11 PM

Quote:

Originally Posted by jbrand540

I recently installed a Steve Wong chip and now after the engine has warmed up it will idle in the 1200+ rpm range.

I have a Wong chip in my '86 (with the 87-89 ECU), and I notice the same thing, but only after about 20 minutes of hard track time.

JB

jbrand540 · 03-08-2008, 07:11 PM

this is after about 20-30 minutes of casual freeway driving. Other then that I really like the chip but I cannot imagine the chip is entirely to blame and feel that is identifying another problem the stock chip was masking. If this was normal of the chip I would think there would be several posts on this.

jimbauman · 03-08-2008, 07:45 PM

It's not normal, but the chip may be trying to compensate for a flaky sensor. Now WHICH sensor is the million dollar question.

JB

jbrand540 · 03-09-2008, 08:03 AM

Does anyone have suggestions on what I should be looking it at. The engine does idle very nicely but after driving for 20-30 minutes the idle will stay at around 11-1200.

Lorenfb · 10:20 AM

"Does anyone have suggestions on what I should be looking it at."

So, put the stock chip back in, as the idle was O.K. prior to installation
of the so-called performance chip, right? Don't waste time and money
looking for a non-existent problem. What do you expect when tuners
"push the timing" beyond what Porsche/Bosch originally tuned the
engine for?

Check here for more insights:

www.systemsc.com/tests.htm

Bottom line: Return the performance (?) chip and get your money back
and leave well enough alone!

"I notice the same thing, but only after about 20 minutes of hard track time."

And another case!!!!!!!!! Great isn't it, i.e. those Mickey Mouse mods?

Note: Make sure that the idle switch is closing, i.e. check the continuity between pins 2 & 5
of the DME ECM connector.

Nine9six · Nine9six's Garage

Quote:

Originally Posted by jbrand540

I recently installed a Steve Wong chip and now after the engine has warmed up it will idle in the 1200+ rpm range. Could this be the CHT sensor? It checks fine with a voltmeter, however, I have the older single CHT. I have read on issues before where high-idle was caused by a faulty CHT.

Before the car gets up to full operating temparuter it will idle just below 1000 and the idle is rock steady. I tried adjusting the idle to counter this and currently have the idle screw all the way in which has lowered the idle to just below 1000 rpm, however, once fully warm the idle will still shoot up to the 1200 range.

Call or email Steve Wong regarding your symptoms. He has ALWAYS stood behind his product.

jbrand540 · 03-09-2008, 10:12 AM

I just got done emailing him. Hopefully he will have some suggestions.

jbrand540 · 03-10-2008, 08:23 AM

At this point I have tried putting the stock chip back and found that idle is till around 950-1000 with stock chip when car is warm. I did not take it for a long enough drive to confirm if car idled up later on. It appears thought that my idle speed is way to high. Currently my idle adjustment screw is all the way in so I believe I have something else going on which is causing me not to be able to lower the idle into allowable limits.

So far I have tested all of the sensors and everything is functioning as it should be. I have tested
1. Idle switch
2. Throttle cable adjustment
3. Full throttle switch
4. O2 sensor
5. AFM, (including barn door output voltages and all 10 locations)
6. ICV valve
7. CHT(test correct with VM when connected to a good ground, this is single wire plug)
8. Visually inspected all hoses and everything is connected and appears tight

Any suggestions as to what I should be looking at? I am going to go ahead and swap out the CHT for the newer two-wire as I was planning to do this eventually anyway, but could this cause this issue?

Nine9six · Nine9six's Garage

jbrand540,
Is there any chance you can more precisely characterize the symptoms...
Surging or hunting idle, or is it a stable high idle?
Did the car exhibit high idle issues before swapping the chip?
Put the OEM chip back in and warm the car properly to see if the high idle goes away once the car is warmed up.
Quick checks include ICV voltages, cleaning, and mechanical movement.
I had a hunting or surging idle problem that I rectified after checking the ICV, and AFM...It wound up being a bad o2 sensor.

84porsche9113.2 · 02:52 PM

This sounds like it could be an improperly adusted or non-working throttle position sensor (TPS). There are some threads on how to adjust it.

Basically when the throttle plate is about to go open, a slight movement of the linkage will cause a micro switch to be deactivated. I think this signals to the car when it is "off-idle". You should be able to push on throttle linkage and hear a slight click before the plate opens. Also, if you have a continuity meter connected to the TPS switch the value should change when the click is heard. The reverse is true, when the car comes off throttle, the plate closes and the microswitch is activated signaling the computer that the car is now idling.

I'm not sure if this is your problem, but I noticed on my car when it was imporoperly adjusted (TPS was open at idle) the car would idle way too high.

Something is defnitely wrong in your car since I don't think your idle adjustment screw should be all the way in for it to idle properly... It seems you are overcompensating for the real problem by using the idle adjustment screw all the way in like that.

by the way, you can test this theory by getting a small screwdriver and closing the TPS manually when your car is at idle. If you are able to and the idle drops you know it is the TPS. obviously this won't work if your TPS is bad, but you may be able to jumper the cable connector with a piece of wire to simulate a closed switch if it the TPS is not working.

Lorenfb · 03-10-2008, 06:04 PM

1. Idle switch - Can cause the problem and MUST be tested at the ECM connector (pins 2 & 5).
2. Throttle cable adjustment - Can cause it. Check the cables.
3. Full throttle switch - Can't cause it.
4. O2 sensor - Can't cause it.
5. AFM, (including barn door output voltages and all 10 locations) - Can't cause it.
6. ICV valve - Can cause it. Just remove it and close the vane and re-install w/o the connector.
The idle should be very low. Now plug-in the connector. The idle should be normal. If not a bad
ECM or valve.
7. CHT(test correct with VM when connected to a good ground, this is single wire plug) - Can't cause it. Always just bypass it with a paper clip.
8. Visually inspected all hoses and everything is connected and appears tight - Can only cause it if the
air leak bypasses the throttle body or the idle valve.

jbrand540 · 03-10-2008, 06:30 PM

Thank you. I will focus on further testing the ICV and idle connection.

seanmccafferty · 03-11-2008, 03:08 PM

I'm curious. Have you found the source of your high idle?

I have an 84 Carrera and installed the SW chip last fall and have been experiencing the same thing. I just the ran the car in the garage for 15-20 minutes and once warm, the idle varies between 1100-1200 rpm. I haven't done any diagnostic work yet .... I've still got snow piled 4-5 ft high by the driveway so I've been working on other stuff.

Steve W · Steve W's Garage

After installing a chip in the 84-86 Carreras, you'll need to turn down the base idle speed adjustment, as they all are getting programming updated to the 87-89 Carrera idle specifications, and where the base idle speed is set on the earlier cars, can cause the idle to be in the 1000-1050 rpm range if not adjusted. The 84-86 specifications are 800 rpm with idle ignition timing at 2.5 degrees ATDC. The 87-89 specifications are 880 rpm with idle ignition timining at 3.5 degrees BTDC. The combination of a 80 rpm programmed increase, plus 6 additional degrees of timing will increase the base idle speed. See the installation instructions that came with the chip, or see the bottom of the following page:
http://www.911chips.com/dmeconvr.htm

The other reason car's can idle higher, especially after installation of the chip is a intermittent or non functioning idle microswitch. This is typically either caused by a sticky or bad switch, or too tight of a throttle cable. When the switch does not activate, the car does not know to go to idle, and remains in part throttle mode, typically resulting in a idle from 1200-1500 rpm. With the stock chip, the difference with a bad switch is not as prevalent, but it still will idle high.

As a side note, if your car has been run hard and extensively such as at the track, the car can idle for a minute or so about 50-100 rpm higher until the car cools down. This was done intentionally to help with oil circulation and cooling after hard runs, but typically doesn't occur in everyday driving situations. Hope this helps clarify things.

jbrand540 · 03-11-2008, 06:22 PM

I have not had a chance to do anything further testing but plan to dive into this weekend and track this down. I will update the thread when I have resolved the issue. My plan is to perform further tests on the sensors idle speed, ICV, etc bye running the car without them to see how the car behaves to hopefully determine if one is not working as it should.

Sean - As Steve says you need to first check your idle adjustment. In my situation I am unable to lower the idle any further then 1000 when the car is luke warm.

jbrand540 · 03-14-2008, 07:11 PM

Did quite a bit of testing today.

With Stock chip back in and new 2 wire head temp sensor idle is around 1000 when warm with screw all the way in and car starts smoking more and more as it gets warmer, not as much as with the SW chip but still smokes. Believe this is rich running but could be oil even though 3 weeks ago it was not smoking at all. I sprayed some starter fluid about all hoses and intake areas with no change. Unplugging the Idle Switch causes the idle to raise significantly so that appears to work. Likewise removing the head sensor plug causes the engine rmp to rise drastically.

Suspecting the ICV valvle I removed it from the system and blocked off the ICV valvel lines. With the done I am able to adjust the idle below 1000 and the adustment seems to be appropriate. Also smoking appears to be gone this way. Bench testing the ICV by hooking a 9 volt battery to it results in it turning both ways without problem. Hooking it to the car and turning the ignition on results in it turning to half way as it should. However when it is at this halfway point it does twitch every second or so, not sure if this normal?? So the ICV based on all my test appears to work correctly and the ECM appears to be sending signals to it. I am a little unclear on exactly how the ECM hold the ICV valve at the halfway point, perhaps someone can ellaborate so I understand a little better.

I did find that somehow one of my O2 connections had come loose at some point, had just tested this 3 weeks ago. Getting it hooked back up did lessen the smoking and makes my idle fluctuate slightly as it always did with the stock chip. Could this cause the car to run in this matter? Would the SW Chip be more effected by the lack of an O2 then the stock chip would be?

Not sure if this info points to something else? I feel like I am missing something here???

jbrand540 · 03-17-2008, 08:49 AM

Anyone provide any thoughts here? As a further test I pulled the AFM plug with motor idleing and it died almost instantly and fairly smoothly, would this eleminate external air leaks? Is there anyone the ICV can be bad even though it passes all tests?

jbrand540 · 03-17-2008, 09:24 AM

another item I forgot to mention is that with the B & C jumpered if I turn the idle adjustment screw out more then about 1.5 turns the idle begins surging between 800-1100 and gets worse as I take the screw out. With out the jumper the idle is smooth at about 1000-1100 if I have the adjusment screw about .5 turns out. If I close the adjusment all the way idle is about 900-1000 but oscillates roughly 100 rpm.