At normal operating temp idles high. Must blip it to get it to idle normally

[BReyes]

At normal operating temp (or when good and hot [car doesn't run excessively hot) especially) idles high. Must blip it to get it to idle normally. Idle control valve replaced. I have it serviced by exclusively by Porsche expert(s-plural because I moved to another city since purchasing it). The shops have performed routine maintenance.

A little background (to show it has been seen by mechanic over the past year and a half):

Engine has been rebuilt. The car may have a chip as it revs to 7200 easily (although I don't let it rev that much [as per one of my mechanics]). Has K&N air filter. Updated exhaust. Newer fuel pump(I replaced the DME before taking her into shop). As I stated above idle control valve replaced. Newer wires (firebraid type), cap rotor. Stainless steel braised fuel line on engine. Newer Alignement. Newer tires. Newer starter. When I say newer I mean new, but replaced several thousand miles ago.

During the replacement of the fuel line, my regular (Porsche racing/service specialists) shop worked on the car(the tech was owner's son (also an expert). I was content with him being the mechanic although I was expecting to have another tech (who had worked on one of my previous 911's ['83's 3.0 with CIS]) work on it. Tech forgot to put "idle tensioning spring" back on. We had determined this but as engine was hot, I personally reinstalled the spring the next day. I mention this because I was expecting the shop to pull the intake off and work on fuel line from above (as advised by a service advisor [if I recall correctly] at shop [also Porsche racing/service specialists) that replaced my fuel pump [I was out of town when that happenned so that is why used two shops] that that was how fuel line would be replaced. I am wondering if by dropping down the engine (not removing it- just dropping it down), as the owner's son did, he caused a problem with the throttle cable.

The car had slight clutch chatter first discussed with service advisor (that I noticed mostly in reverse, and then later progressed to an "actual problem") at that time of the fuel pump replacement, but was minimal. The clutch was replaced very recently (This time by still another shop-yes that's right-I moved to another city), and they also adjusted valves, replaced plugs, valve cover gaskets.

The problem did not go away with the install of the "tensioning spring"( the little spring that provides tension to bring it back to idle, or the clutch replacement (I was patiently hoping that it would go away finally at that point). I drive it on the highway alot. It is a daily driver and runs very nice and all mechanics complement me on the condition of the cosmetics ad mechanics of the car.

Is this problem due to throttle cable is bent? I don't think it is because before it gets up to operating temperature it doesn't do this. I cant find previous posts here discussing this problem.

Remember, when I push the clutch in order to come to a stop at a stop light, the idle goes up to about 1500-1800. I blip it and it idles fine every time.

Tired of blipping it. I am the type of Porsche enthusiast that is interested in fixing my own Porsche or at least diagnosing the problem. If I cant diagnose it I get upset. I don't mind letting the experts fix it, but I like to know what it needs before turning it over to a tech.

Hope I was not bantering above.

Thanks in advance for your help guys. Hope to see all of you at Sebring this year (HSR next week and the 12 hours on the 19th). I know I probably have seen some of you at Rennsport Reunion II, Daytona, or Sebring in the past. One day hope to get a race car, for club and vintage racing, and then am sure I will meet some of you.

Best Regards,

[ausdilecce]

First off, lets just see what the throttle is doing when the engine is off.. (checking linkages )

Get in car ( with engine off ) and press accel to about midway, then release as you normally would ( as you are coming to a stop light, say )

Then get out of the car and look at the throttle position on the engine.. can you push the throttle to the normal idle position or is it already there ? ( if you can push it, you have a throttle linkage binding issue )

BTW, there is a microswitch that tells the motrnic system that the throttle is in 'idle' mode.. you will hear an audible click as you move the throttle ( manually, on the engine ) into and out of the idle position.. So, by depressing the accelerator and releasing, you are checking whether the spring(s) have enough tension to press in that microswitch..

Good luck

[NOH20]

I had the exact same problem on my '86 Carrera. Turned out that the cruise control linkage was too tight which didn't allow the micro switch to "engage." I loosend the cruise cable and Viola, the problem went away.

[avi8torny]

I just had this problem with my 87 Targa.....I sprayed some lube were the throttle linkage disappears in the throttle body and worked it back and forth. It was pretty gumbed up. Runs like a champ and idles perfectly.

[scottb]

Also, check your mixture.

[BReyes]

Ausdilecce:

-I have (previously) removed the wooden kick plate under the accelerator pedal.
-I opened hood and checked throttle to see it is at idle.
-I depressed the pedal half way, and checked the throttle position on the engine. It seems to be returning back to idle position.

Note: the pedal does not return all the way up (e.g. as far as it could come up by me manually lifting it with my hand). I am not sure if that is normal to stay about 1/2 inch or so from it's highest possible position. Also note that if I start engine (car is cold as it hasn't been driven today) with my head down by the accellerator pedal, i notice that pedal is automaticaly depressed about 1/8 to 1/4 inch (I tried it twice to be sure and it did this each time)

-I started engine and tried to make it rev a little higher by depressing the throttle at the engine slightly. I can (not remarkably) get it to idle high by getting the throttle to stay more open at the engine. I notice that by depressing the throttle at the engine by about 1/64 inch or so it idles 1300-1500. It is is such a small amount (aprox 1/64 in.) that needs to come up to close the throttle. I am thinking the spring needs more tension.

note: I did not hear the click that you mention with engine off and key off; with engine off, and key to acc position; with engine running and me at the engine moving the throttle.

AVI8TORNY:
I sprayed some lube (again). Had previusly used lithium grease at the acceleraor pedal. Used WD40 on the engine at the throttle and where linkage disappears down behind engine. I can't see very well back there however. I will retry to lube it again too.

SCOTTB:
I asked my serive advisor (last month [during service]) to check the mixture. I asked him to make sure that throttle cable is fine and that car is performing to its max potential. I was told (if I remember his words exactly) during/after mechanic worked on the car "mixture is computer controlled. It is fine. The engine runs great!" He also drove the car and noticed no problems with the car. As I know it is not CIS (as in my '83) and servicing EFI on '87 doesn't involve all that complicated stuff the CIS does. But I digress.

I too have thought mixture may be too rich as the tail pipe is black inside. But then again I know this is not one of my muscle cars from high school. And based on discussions with service advisor(s)/tech(s), it is supposed to be a little black. It is not excessively black (it is slightly powdery), nor wet, nor has fuel smell when I rub finger inside tail pipe tip. Scott: p.s.: must be nice when in the Bell( I am FAA certified, private single engine land, but one day would also like to pilot a copter.

Thanks guys.

I am going to try to add tension to the spring (wire a few of its coils together) and drop the top and drive it into stop and go traffic to see if still idles high. Will also go to NAPA for a spring, but am not so confident NAPA will have one that I need. I am in Key West, 150 miles from nearest Porsche dealer.

Once I do this, I will post what transpired.

Best Regards,

[scottb]

Originally posted by BReyes
SCOTTB:
I asked my serive advisor (last month [during service]) to check the mixture. I asked him to make sure that throttle cable is fine and that car is performing to its max potential. I was told (if I remember his words exactly) during/after mechanic worked on the car "mixture is computer controlled. It is fine. The engine runs great!" He also drove the car and noticed no problems with the car. As I know it is not CIS (as in my '83) and servicing EFI on '87 doesn't involve all that complicated stuff the CIS does. But I digress.

I too have thought mixture may be too rich as the tail pipe is black inside. But then again I know this is not one of my muscle cars from high school. And based on discussions with service advisor(s)/tech(s), it is supposed to be a little black. It is not excessively black (it is slightly powdery), nor wet, nor has fuel smell when I rub finger inside tail pipe tip. Scott: p.s.: must be nice when in the Bell( I am FAA certified, private single engine land, but one day would also like to pilot a copter.

My understanding is that the mixture is adjustable, and when I had my idle problem a mixture adjustment cured it. Maybe it's time to try a new mechanic....

[ausdilecce]

Originally posted by BReyes
-I started engine and tried to make it rev a little higher by depressing the throttle at the engine slightly. I can (not remarkably) get it to idle high by getting the throttle to stay more open at the engine. I notice that by depressing the throttle at the engine by about 1/64 inch or so it idles 1300-1500. It is is such a small amount (aprox 1/64 in.) that needs to come up to close the throttle. I am thinking the spring needs more tension.

That increase to 1300-1500 from idle of about 880 *is* the result of the throttle releaseing the microswitch ( so computer knows for sure its off-idle ), so either
1) fit a stiffer spring
2) adjust the microswitch position
3) adjust the lower stop on the throttle

( I would opt for option 1 )

Originally posted by BReyes
note: I did not hear the click that you mention with engine off and key off; with engine off, and key to acc position; with engine running and me at the engine moving the throttle.

This click is kinda like a relay click but not near as loud.. You should hear it ( with key off, engine off ) when you move the throttle that 1/64 from the stop and back.


Ohh, and motronic's mixture is certainly adjustable.. Computer controls the mixture a bit ( to account for air temp/ altitude/ load etc ) but major adjustment is performed by adjusting the mixture screw on the air meter box ( and the spring *inside* the air meter box )

[BReyes]

Gentlemen:
I went for a ride after stiffening the spring. Nice drive but the problem recurrs once it gets to normal operating temperature. I will get to the bottom of this soon enough though. All your comments are very much appreciated. For the most part, I like my mechanic(s) (you those guys that have all the Porsches in their shop, and the lifts, and special tools), but they are merely human like us. The only difference is they are on the clock so I take it easy with them, and I am self trained (sort to speak. I do ok, and am getting better and better as time goes by) and I have les tools now than I used to (a friend's grandmother passed on while I had my tools at her house while in college and they were lost). As I gain more experience, I will more quickly be able to coroborate what they say with what I have learned. The biggest problem is that the mechanics have told me that the manuals are very expensive (one even told me once that they just paid $10,000 for a 996 manual(CD or volumes [i don't recall if it was both]).

I will be looking into the (1) "microswitch", and (2) mixture more closely next

NOH2O:

I will look at that tomorrow, and although it looks loose enough (I just forgot to post to you last time [I wasn't ignoring you]), now that I think about it more, I see what you mean.

SCOTTB:

I will consider the mixture issue again tomorrow, and vaguely recalling the information I read on other posts, I also notice a surge of about 50 -100 rpm too, so that may be another sign. I will read them again tonight .

I have not heard the click of the relay/microswitch today, but will continue seeking it again tomorrow.

AUSDILESSE:
I will read up on Motronic mixture adjustment, and consider my options. Either way, their is no mechanic nearby to take it to tomorrow. You mention the relay/microswitch, screw on air meter box, and spring inside, so I will certainly look more into that.

Thank You.

Regards,

[ausdilecce]

BReyes,

PLEASE NOTE, one should not 'play' with the mixture control screw OR the spring in the air meter. Both of these are set with the aid of a gas analyser ( which you probably don't have ) under very strict conditions.. If you set either of these incorrectly, bad running or *no* running WILL result. I would think that your issue is a linkage binding issue and NOT an incorrect mixture issue.

Try the simple things first..


in this ( somewhat busy ) diagram of the intake bits,

17 is the microswitch
check hoses 28 and 30 and 38 and 14 for cracks/leaks
be sure clamps 22 and 23 are tight
be sure the screw (12 ) that holds the throttle valve switch ( 15 ) is tight

Good luck

[BReyes]

AUSDILECCI:

It is idling well again. The diagram was helpful. I actually did not find any defective parts, nor do I know what I did to fix it. I am starting to think that is normal and probably happens to techs sometimes.

I lubricated the throttle where it goes into the throttle body (it wasn't gummy though). I loosened the cruise control cable (although it was not tight at all). I felt, with my hands, the hoses depicted in the diagram to try to find any problems (all were good). I made sure (I had this before) all bolts and screws were tight. I plugged an unconnected rubber hose covered by soft braided hose approximately 1/4" id coming out of a canister type of part in the upper left side (driver's side) firewall. I cranked engine but it did not have vacuum. I expect it is some thing for an airpump (anti polution) but I dont have airpump as far as I know (I haven't found a cat. No headers but not stock exhaust either. It is louder than my '83 SC was). I cleaned all the metal connections around the throttle body and airflow meter (although not too much more than a little dust) with a toothpick. And lastly but not least, as I was looking for the microswitch (the diagram is somewhat hard to follow), I was making sure the throttle stop (behind [and not visible] the throttle body) was not obstructing its return to full idle position, I felt something and started the clean it with my fingernail. I happend to scrape loose a little plastic rectangular part that looked like somthing I just had broken. I noticed it then as the microswitch and making sure it was clean tried to put it back where it came from. It seemed to go back in just fine, and in fact was not broken.

Tomorrow I will tighten the cruise control a little (although I don't think it works well. Maybe it was too loose in the first place. Maybe not-that is probably something to look into later.), and hit the road to HSR event in Sebring.

Thanks again, everybody.

Regards,

[LeeH]

I had the same problem with my '84. In my case it was the microswitch. Test it with a meter. Just because it's clicking when the throttle is closed does not necessarily mean the contacts are closing.