JCP1990S4

RE: 1990 S4:

Hi Guys I have explained this problem before. It stopped happening but happened again last night.

After running some arrands driving and stopping/starting for quite awhile I stopped and parked the car for about an hour. Got back in and started it up. The cars RPMs dropped and the car wanted to die out. I put it in neutral and kept the gas on to avoid it dieing. I got around the corner and it died out. Then I got it started it again and go on the freeway on ramp and drove at freeway speeds and got off 1.5 miles ahead. Got off freeway and stopped at the red light. Car was acting fine once again. Kept driving it to the Movies and when I pulled into the parking spot and put the car in park the RPM's shot up to 1500 when I put it in park it went back down to normal, put it in park again same thing RPS raised to 1500. Then I shutting it off.

Then 2 hours later I got out of movies drove the car home and it drove as normal and wonderful as can be all the way home into its garage.

This problem happens similar to this every once in awhile. It always happens after restarting the car after it was driven for a while and shut off and restarted anywhere from 2 minutes to 1 hour and its done this "trying to die out thing" The problem has never happened when the car was cold.

This is driving me nuts. Any ideas???

the flyin' scotsman

It sounds like its perhaps heat related but before we go there can you list what maintenance has been done.

JCP1990S4

Car has been extensively maintained since new. Had it to my technician and he could not dupicate the problem....same old story. But he said its possibly some idle part that regulates the idle. Part not expensive but getting to it is. Just thought I would get some opinions.

Dictys

I have a simliar issue which I have traced to the FPR or dampers have a leak in the vacuum, therefore at idle flooding the engine, found some fuel in the vacuum lines.

I have done a top end refresh and replaced all the normal stuff and she ran fine afterwards, then slowly the idle felt rough, then arrived at the stalling issue.

The TBF has been checked and a PKlamp fitted.

This weekend I hope to replace the FPR and dampers and associated vacuum tubes, also fit a fuel pressure gauge.

Hopefuly this will fix the issue.

JCP1990S4

Wow. Let me know what your outcome was. I will have mine gone through as well.

Thanks

Dictys

Well I the car does not stall at idle anymore, but the idle still seems rough, hunting between 600-700 rpm.

I completed the FPR and dampers replacement and associated vacuum tubes and I also fitted a fuel pressure gauge. I get a steady 55 psi at idle. My garage previously did a full intake refresh and replaced the knock sensors and idle control valve.

The car performs great above idle, but i need to get this idle situation sorted as my car sits in traffic everyday.

It will run rougher if I have the A/C and blower on maximum and lights on, then really rough with fogs added to the lights on. If I gently squeeze the throttle to 800 rpm the car is fine.

My blower only seems to work on full speed (i will get a resistor pack to sort this).

The brown ground at the jump point seems frayed, where does this connect to?

I'm now thinking coils or ignition wires, or an alternator issue these don't seem to have been replaced.

Anyone else with any ideas?

Mike Frye

The fuel rail pressure gauge will help isolate or eliminate several things. Best $50 you can spend on your engine for diagnostic and baseline purposes.

I think the idle 'shooting up to 1500' may be a reaction of the car to a low idle/stall condition so it may not be a real symptom of the idle issue you're having.

I'm not so much the S4 guy, but it sounds almost like the problems Steve (Norcoastal) was having with his '87 before it finally gave up and wouldn't start at all. His sounded like it was going to stall and he'd have to put it in neutral at lights so he could keep it running. Other times it would run fine.


We traced it back to a bad fuel pump and once that was replaced it started and ran great.

AO

I like the failing fuel pump idea, but a sticky Idle stabilizer valve could also be the culprit - both for high idle as well as low idle.

Eturbo924

My 1987 was doing a similar thing.

Then the fuel pump failed. So replaced it.

Replaced many other items that did not impact the poor running and stalling. I had high idle and stalling. It would run fine for a period and then stall. It started to get worse and worse until one day it would not restart.

Turned out to be the LH. Once it was replaced the poor running and lack of running was gone but the high idle was still there.

Sooo. Paul Zeus created a plug to go into the area where the ISV feeds air. The plug has a hole in it that allows just the right amount of air to flow through it to keep the idle around 900rpms. It drops to around 750 when in D.

We had to play with the hole size to get it where I wanted the idle. 1500rpms was too much

Anyway not saying for sure that is your issue... just sharing my 2 cents.

SteveG

So . . . . this is a fix for a bad ISV?? and you placed an choke or air flow governor device that basically sets the idle at 900 and takes the ISV out of the system, assuming it is stuck at some position and stays there?? Does this allow the car to cold start normally? A picture would be great if it is accessible.

JCP1990S4

I was probably not very clear on my issue.

My car runs wonderfully 95% of the time.

Then all of a sudden it will freak out on me.

Everytime it happens its is the same scenerio. It will be running fine and I will shut if off after driving and then restart it shortly after while its still warm. It will want to die out and then when I force it to stay started by reeving motor or driving it (nonstop) for a few minutes. Then it will clear up and the idle will be fine. but if I put it into park the rpm's shoot up to 1500 and if I put it back into drive it will go back down to normal, then if I put it in park again it will shoot up to 1500 again. If I shut it off let it get cool (not meaning that is was running hott) for several hours and start it up, it start up like it never had a problem.

This last time it happened, I stopped and started 5 times making short errands over a 2 hour period of time. Then one lucky time the issue reared its evil head once again.

This has never happened when the car was cold. only warm and after it was recently shut off and restarted again shortly thereafter.

The last time it happened ( 2 months ago) I drove the car from LA to Las Vegas with not a issue. Even stopped once. When I got to Vegas I needed gas. Pulled over put gas in and after I started it up....it started doing the same BS again. I was able to get it to not die out but it was not easy.

Many times it has done this same thing over the years. A few of the times I was unable to keep it running and wind up draining the battery trying to start it. One of the times it wound up needing a fuel pump. Maybe I burnt it out.

Just a pain in the butt. Kind of takes the joy out of owning it.

the flyin' scotsman

ok............what age are the MAF, LH ECU and the ISV?

Has the intake ever been off for refresh?

JCP1990S4

I don't think that it has had a refresh.

What does that include and what kind of $ am I looking at having that done?

the flyin' scotsman

Not suggesting the intake is the issue just trying to narrow down what maintenance has been done.

If the intake hasn't been removed can we assume that the fuel injectors, ISV, all associated gaskets and the MAF are original?

When the idle is at 1500 rpm is it stable or surging?

JCP1990S4

The idle just will sit there at 1500. Now if I went out in the garage right now and started the car it would go up to maybe 1100 and work its way down while warming up. I think this high idle issue only happens in conjuction with the dieing out issue.