Surging idle at cold start up

[911kiwi]

Car: 1984 911 Carerra.
Problem: At cold start up - the idle surges, as if you are pumping the accelerator pedal. Depressing the pedal to move away smooths it out, but once the car is left to idle again, it resumes.
Tried: Swapping out the ECU with known "good" one - no change, so assume ECU is OK.
When warmed up, the idle is fine.

Has anyone had this problem and how did you correct it?

Cheers,

[pete3799]

Mine suffers the same fate.
Surges when cold idles perfect when warm.
Think it's a little rich but i'm sure someone better qualifided will chime in.

[scotricker]

there have been a bunch of threads on cold start issues,and idle, I searched them all, then never did the fixing,,,, so I still surge idle until warm. Maybe I should get around to fixing that, too.

[DonMo]

9 times out of 10 it is fuel mixture. You have a leak somewhere that is making you lean out.

check this out , Loren and Steve Wong give good info to get rid of the hunting.

Carrera 3.2 idle fluctuation

[scarceller]

Mine also surges at cold start (below 50F).

I have been changing and playing with my cold start maps in my chip lately (I burn my own chips) and found some interesting things about cold start and surging.

1) To much fuel at cold start will cause surging, I know this because I intentionally richend the cold start fuel map.
2) But the real issue is to much Ignition Advance at cold start! Turns out our 84-89 cars advance ignition with temps lower than 48F. They start advancing ignition starting at 48F all the way down to -25F and at -25F they add 18degrees advance! that's in a 87 chip. What I did was back off the ignition advance and the surging stopped, at least in my car.

I think the engineers did this to warm the car quickly at very cold starts. The idea is to add ign adv while cold to produce more torque and thus increase heat.

The bad news is the only way to reduce the amount of ign advance during cold start is with a altered chip.

[1990C4S]

I fixed my idle with a Steve Wong chip. Just another benefit of an aftermarket chip....

[scottb]

I had a similar problem in my 84. A simple mixture adjustment was all it needed. Problem solved!

[scarceller]

Yes, for sure always check the basics first. Start by checking base mixture as a rich base can cause surging.

I only wanted to explain the effects of to much fuel or to much ign adv during cold start. My car is not stock so my issue most likely could be out of the norm.

[vulcan300]

Search on "hunting idle" and you will find many threads that cover this topic.

[Bearded Viking]

Lot's of good info in this thread... Start reading.

idle bounce

[efhughes3]

Originally Posted by 1990C4S

I fixed my idle with a Steve Wong chip. Just another benefit of an aftermarket chip....

A chip can actually make it worse, IMO. If there is a problem, there is a problem.

[Sean Hamilton]

Originally Posted by 911kiwi

Car: 1984 911 Carerra.
Problem: At cold start up - the idle surges, as if you are pumping the accelerator pedal.................Has anyone had this problem and how did you correct it?

Yep !!, plug the AAV valve ! AAV and Decel Valve

[1990C4S]

Originally Posted by efhughes3

A chip can actually make it worse, IMO. If there is a problem, there is a problem.

My idle is much smoother with a chip. So is my friend's car.

Maybe this is useful:

Idle Hunting -- The problem continues!!