Idle question

[david.avrahami@]

1987 Carrera...
I start the car and it idles at approx 1100 rpm and as it's warming up, it reduces to approx 780, slightly rough idle, and it settles when engine is warm at 880 and steady.
I was told before that this is quite normal...
My question is: Why can it not go slowly from 1100 rpm to 880 and stay there?
Can this be corrected? How?

[emac]

David- I have a 81 so I'm not sure I can help but I blocked off my decel valve and this took care of the issue.
Ernie

[david.avrahami@]

1. What is a decel valve?

2. when I open the oil cap, engine is warm, idle goes down to below 800

[david.avrahami@]

Where do I block the decel valve? a picture will be well appreciated...Thanks

[david.avrahami@]

I do not believe there is a decel valve in a 1987...
there is , however, an ICV, IDLE CONTROL VALVE,
I think that it an essential component and can not be blocked....but it can be cleaned.
Do you think that this might do it?

[Nostril Cheese]

I dont think the '87s had a decel valve either.

You should take the ICV out and clean only the mechanical portion with carb cleaner.

Then inspect ALL the vacuum hoses. If they are hard or cracked, replace them.

Alo think about replacing the O2 sensor if it hasnt been done in a long time.

[Por_sha911]

If the idle drops when you remove the oil cap you don't have a leak. If there is no leak, replacement is a good preventative maintenance but it won't fix your problem.
Clean the ICV. Very easy and costs virtually nothing.
O2 replacement is not a bad idea but not cheap. You may want to do the above first. If the problem still remains, disconnect the O2 and see if the problem persists. If there is no noticeable difference then look for other causes.
BTW, have you base-lined your car? How clean is the air filter? How old are the plugs wires? These things won't cause what you describe but they can accentuate a poor running issue.

[david.avrahami@]

1987 CARRERA...answering your questions....I just finished changing dist. cap & rotor, repl, aced plugs and wire set (Magnecor kv-85), changed oil&filter, replaced air filter,
and yesterday removed and cleaned the ICV.
The idle from cold start seems to have changed somewhat...it stays at approx 1100 rpm longer and start going down as the engine warms up but it will go BELOW 800 RPM, AS BEFORE and only when fully warm, will settle at 880 rpm....but the overall idle seems smoother...
Any additional thoughts on remedying the below 800 rpm issue?

[Rich Gas]

This may seem too simple, but put a new seal on the oil cap...

[david.avrahami@]

Thank you all for responding but I do not believe you answered the issue here...
Please revisit my initial question on the first thread...

[Rich Gas]

David, it could be a number of things... Your car is old, seals and gaskets dry up and shrink...thus vacuum leaks. The ECM collects data from a number of inputs, O2 sensor, CHT, speed and reference sensors, which all could be failing in some way. Your fuel delivery system could be clogged or off pressure... Injectors, fuel filter, fuel pump, fuel lines brittle and leaking.

I would check for vacuum leaks in the obvious places: brake booster line, oil cap seal, manifold gaskets.
I would check my fuel delivery system next: injectors, filter, pump and lines.
I would check my sensors next: O2, CHT, speed and reference.
You replaced cap,rotor, wires (check these connections), plugs etc. Coil?

Be systematic.

I did all these things and my car still runs EXACTLY like you describe. Hits 1100, comes down under 800, runs rough until warm, then runs perfect.

Try setting your base Idle again...
Try setting your mixture properly.
Are you running a chip? Find out.

Etc etc etc

[inthedoghouse]

My 85 does the same thing. Fires up quickly and stays around 1100. After a block or 2 of driving it drops below 800 and is slightly rough. After its warm it settles in nicely at 880 per my SW chip.

I agree it would be nice to smoothly lower from cold idle to 880 but its pretty low on my list of things to troubleshoot

[ischmitz]

Your car's engine is controlled by a DME. It uses the intake temperature and the CHT to determine how much the mixture needs to be enriched during the cold-start phase. A cold engine will trap more fuel vapors on the inner walls of the intake track and thus the requirement for a richer mixture. The DME has a map that tells it how to adjust the mixture based on the measured temperatures.

If you have a slight vacuum leak your mixture will be off. While the DME can compensate this to some extend it requires the O2 sensor. During cold-start the sensor isn't yet warmed up and won't help much. An aged sensor has a slower response and further compromizes the ability to correct the mixure.

Once the sensor is at operating temperature it will adjust the mixture to compensate for the leak. To improve I would check:

- vacuum leaks in intake
- O2 sensor responsiveness (as they age they get slow)
- ICV (clean it with brake cleaner)
- valve adjustment

Ingo

[stlrj]

Start with the basics. Have the idle mixture and base idle speed checked.

Don't assume anything.

[david.avrahami@]

Great detailed responses that make lots of sense...thank you all!!!

[HorstP]

David. Exactely same issue here. I started to get used to it.My ICV is new and I did set base idle by the book. My guess there is a vacuum leak somewhere at cold temperatures. But instead of chasing it, I left it for the time being. Let me know if you find something.

[Josh D]

I'm not sure how sophisticated motronic is to idle control, but 80 rpm between end of cold start initiation and totally warmed up engine is not that big of a deal.

It could simply be a matter of oil temperature and resistance to flow when cold. Until the engine oil reaches normal operating temperature, the resistance to flow will cause additional drag and slow the engine down. Whether or not motronic can compensate for this with idle control, I don't know. CIS sure doesn't.

Do a correlation between oil pressure and idle speed between cold and normal running temp. Oil pressure will be high at idle when cold, and will drop at idle when warm/hot.