dlpalumbo

My '90 C4 has always (for the 3.5 years I've owned it) suffered from an idle bounce. That is, when I lift the throttle with clutch disengaged, the idle will fall below the 850 RPM point then bounce back up. Its as if the ECU doesn't have a good guess at what the idle valve opening should be. Sometimes it will even stall. I've gone the usual route in addressing this issue and decided, at last to replace the valve.

As you may know, the valve is $320 through Pelican. I found some folks offering $260 and one offering the valve at $150. I decided to try the $150 part as it looked identical in pictures and I figured I'd compare the one on the car with the replacement to make sure it matched before I put it in.

Well, the replacement had the same Bosch part number so I installed it. As I was expecting, there was very little change in the idle behavior. However I became suspicious that the valve might have been replaced by the PO with the cheaper unit so I decided to see if I could read the part number of the more expensive parts from their web pages.

The part numbers matched except for the last 3 digits. My ICVs end in 514. Pelican's and others in the $300 price range end in 531.

Has anyone replaced their ICV (ISV) with an aftermarket unit of a different part number and had a similar idle issue??

Cheers,

Dan

sml

'90 C4 - same problem. Would love to get it fixed.

Tried:
- cleaned DME until it rattles when shaken - no change
- replacement steve wong chip - no change

There are some other threads here, where someone has suggested to check all intake connections for air leaks. I tried this but didn't have much luck with access to all the fittings

Other ideas noted from previous threads here:
- vacuum leaks
- MAF
- idle switch and FT switch on the throttle body
- DME adaptation
- cylinder head temp sensor (dont think it is this as mine was replaced by the previous owner)

If you've tried two, I dont think the ISV is the cause of your problem.

dlpalumbo

The question is whether this aftermarket ISV with the 514 part number is somehow calibrated differently than the 531 part. There is an adjustment on these things. Its also possible that the internals could be different, e.g. a different spring or motor.

Could you pull your ISV and check the part number? If its the 514 part, then it supports the theory that this part is causing the problem.

sml

Just removed the 20yr old 514 ISV and installed a brand new 531 ISV.

I did not reset the battery to clear the DME adaptation settings. Perhaps I should try.

There was no difference in the small idle bounce nor any differences in whilst driving / idling.

silverboy

Mine had the same problem a few days ago. Cleaned the ISV & voila - it's fixed. No hunting.

sml

Tried resetting the DME with the battery disconnection method.
No luck.
Exactly the same as before.
Slight idle bounce (400rpm to 1000rpm to 800rpm).
Guess I'll learn to live with it.
Old 514 ISV to go onto ebay.

964Patrick

Sounds familiar, until recently had the same problem. What I did:
- Cleaned the airbox
- Cleaned the air flow meter
- Cleaned the idle speed valve
- Replaced the seal between airbox and airflow meter
- Replaced the DME relay (I think the old one was still good but i needed a spare anyway)
- Fixed a leaking connection on the distributor vent hose
- Futile attempt at cleaning parts in the engine bay while I was in there :-)

Solved my problem, rock steady idle and much smoother acceleration.

sml

Spent a few hours yesterday cleaning the AFM.
I did not replace the seal between the airbox and AFM but did tighten the bolts.
Replaced O2 sensor a month ago.
Replaced ISV a few days ago.
Steve Wong chip.
Checked most of the intake connections.
Still has a bounce.
Not sure if I have LFW or not.

964Patrick

You might also want to check this technical service bulletin regarding the airflow meter connector:
http://www.pcarworkshop.com/images/b...0590geolab.pdf