Occillating idle

Ed Sato · 03-25-2004, 07:38 PM

Hello
I am having problems with my idle in my 84' Carrera. The idle is kind of erratic when the engine is hot. It seems to occillate and sounds like wah wah wah............... going up and down between 500 - 1000 rpms. I have cleaned the idle regulator and it did not help. Any suggestions? Thanks for any help that any can offer. Wayne I live on Oahu maybe you can check my car out when you are here. Just joking!

If you need suggestions on where to go email me. I may be able to give you a tour even. Aloha, Ed Sato

bigchillcar · bigchillcar's Garage

ed,
any recent work done on the car that could lend a clue as to what the problem is?

few things:
dirty injectors could cause it...run some techron through the system.

sticking airflow sensor plate...remove the big rubber boot on top and check for binding.

leaking cold start valve...would cause excessively rich mixture, rough idle.

lambda sensor (oxygen sensor)...sending wrong air/fuel ratio data to computer, thus causing rough idle.

ryan

Jeff Alton · 03-25-2004, 08:10 PM

Could be a vacuum leak. I do not think you have a sensor plate or a cold start valve, I think they were not longer required with motronic.
Could also be a mixture adjustment.
To check the O2 sensor, simply unplug it and see if the idle cahnges.

Jeff

scottb · 03-25-2004, 11:04 PM

Ed:

I have an 84, and had the exact same problem. I replaced the O2 sensor, the head temp sensor and the idle control valve. No joy.

Then someone suggested that I get the mixture adjusted. I took the car to my friends at TRE. They adjusted the mixture, and I haven't had a problem since.

So, before you go and start investing lots of money in what may be unnecessary parts, have your Pcar wrench tweak the mixture.

Let us know how it goes.

tcj · 03-26-2004, 08:47 AM

Had also very similar problems with my European -84. Hence, no emission control or O2 sensor. As with Scott, adjusting the mixture and checking all wire connections in the engine room cured the problem.

/TcJ

lparker · 03-26-2004, 12:54 PM

Quote:

Originally posted by scottb
Ed:

I have an 84, and had the exact same problem. I replaced the O2 sensor, the head temp sensor and the idle control valve. No joy.

Then someone suggested that I get the mixture adjusted. I took the car to my friends at TRE. They adjusted the mixture, and I haven't had a problem since.

So, before you go and start investing lots of money in what may be unnecessary parts, have your Pcar wrench tweak the mixture.

Let us know how it goes.

Any idea how they adjusted the mixture?

I'm having the same problem with my car but the fluctuation isn't bad. It's +/- 100rpm of 850.

twin plugged targa · twin plugged targa's Garage

The mixture is really easy to adjust- If i could only remember exactly where that screw is .
But I do remember that it is important to remember how many turns out, the original setting was.
1st you tighten the screw all the way in and then undo it between 5-8 turns depending on how lean rich you want.

Maybe someone could chime in for more info or post a pic of the intake for the 3.2 Carerras - it may jog my memory

I had fluctuating revs and removed the O2 sensor then cleaned it with a green scotch brite pad and brake cleaner- worked for my O2 sensor and the revs!.

john walker's workshop · 03-26-2004, 02:49 PM

try just lowering the idle speed first before getting into mixture changes. do it hot, at idle, by turning the adjuster that's in the center/rearward side of the throttle housing. it may have a yellow plastic tamper guard on it, which will have to be broken/pryed off. then use a 7mm deep socket. clockwise to slow. too high an idle speed tends to cause the surging you described. shoot for 800 rpm.

lparker · 03-26-2004, 03:10 PM

This is not something i've attempted before. Would anyone have pics to point me in the right direction?

KTL · 03-26-2004, 08:42 PM

Quote:

Originally posted by lparker
This is not something i've attempted before. Would anyone have pics to point me in the right direction?

Picture of where the idle screw is located can be found here:

3.2 cold start problems.

Here's a couple of topics that discuss how to adjust the idle on a Motronic Carrera:

3.2 Idle Speed Adjustment ????

3.2 Idle Problem

The socket that you must bridge in the engine bay, that is mentioned in the above topics, is behind the black plastic cover on the driver's side of the engine bay. It looks like this (picture courtesy of SteveW):

lparker · 03-26-2004, 09:08 PM

Once again, thanks Kevin.

ChrisBennet · ChrisBennet's Garage

Picture of the week

Jon Hile · 03-27-2004, 06:17 AM

I also had this same problem. Took off the ISV, sprayed it out with carb cleaner, shook it around a bit to free up the silver baffles inside, drained it out then gave it a shot of compressed air (to clear out the carb cleaner). Last I shot the inside with a little WD-40. Problem solved. This "fix" lasted about two years, where every six months or so I would have to do it again. (I was carrying around a small can of carb cleaner and WD-40 just in case it acted up on the road.) Finally coughed up the $100 and got a new ISV about two years ago.

Jon Hile · 03-27-2004, 06:19 AM

Whoops, I now see you already tried that! Guess I should learn to read rather than skim.

stlrj · 03-27-2004, 07:56 AM

I agree with John Walker's advice, you need to lower your base idle speed with a 7mm socket and it can be done without bridging B and C.

Ed Sato · 04-05-2004, 11:11 PM

Hello everyone
Sorry for not thanking you all earlier but I had one hell of a busy week last week. I still haven't read thoroughly through all your posts but I will try to get to it this week and try all of your suggestions. Once again thanks to all of you for your help and hope to return the help someday. Aloha, Ed
P.S. I will repost the solution when I get it fixed.