Stumbling idle after driving
Banned
Joined: Jun 2005
Posts: 4,023
Likes: 724
From: NJ but from Boston
Gents,
My 86S does the same thing with the following exceptions:
Sometimes starts hard(2-3 cranks before catching).
Runs great except when idling along in traffic between 1000-1400 rpm. At those slow speeds it starts to buck or surge slightly. Once the rpm's go above 1500 it smooths out.
The most noticible rough idle occurs at stoplights. The car starts to buck or the idle drops out just like it is about to stall-it never does stall though.
It's very annoying.
Thanks Rich
My 86S does the same thing with the following exceptions:
Sometimes starts hard(2-3 cranks before catching).
Runs great except when idling along in traffic between 1000-1400 rpm. At those slow speeds it starts to buck or surge slightly. Once the rpm's go above 1500 it smooths out.
The most noticible rough idle occurs at stoplights. The car starts to buck or the idle drops out just like it is about to stall-it never does stall though.
It's very annoying.
Thanks Rich
Three Wheelin'
Joined: Sep 2002
Posts: 1,477
Likes: 2
From: No Turbo, No SC
John, in regards to 928 S4 cars with GT cams and automatic trans, I can't help but wonder if the programming for the EZK and LH could be changed to make up the difference?
Maybe take the Auto trans chips and change the RPM, fuel and timing parameters to match the GT chip set.
FWIW, I sent you my MAF last week and you should be getting it in a few day!
Maybe take the Auto trans chips and change the RPM, fuel and timing parameters to match the GT chip set.
FWIW, I sent you my MAF last week and you should be getting it in a few day!
Rennlist Member
Joined: Feb 2002
Posts: 7,060
Likes: 42
From: Cambridge England
Hi Rich,
How many miles on your car ?
Hi Curtis
OK your LH ECU is getting lonely, it will be happy to see your MAF again :-)
I am sure it is possible to modify the chips as you say. I'm sure that making the GT chips ilde adapt correctly to "D" and "N" would not be difficult.
As Malcolm reports good results from using GT chips in an auto S4, maybe I should do this !
I'll let you know as soon as your MAF arrives.
Regards
How many miles on your car ?
Hi Curtis
OK your LH ECU is getting lonely, it will be happy to see your MAF again :-)
I am sure it is possible to modify the chips as you say. I'm sure that making the GT chips ilde adapt correctly to "D" and "N" would not be difficult.
As Malcolm reports good results from using GT chips in an auto S4, maybe I should do this !
I'll let you know as soon as your MAF arrives.
Regards
Banned
Joined: Jun 2005
Posts: 4,023
Likes: 724
From: NJ but from Boston
John,
only 63k on the car. The previous (original ownwer) stored it in a warehouse in Georgia the last 4 years once he decided not to put any more money into it.
I had to replace all the rubber hoses etc., due to dry rot from the southern climate.
I also added the Autothority two chip set up. Other than that it is stock.
Thanks Rich
only 63k on the car. The previous (original ownwer) stored it in a warehouse in Georgia the last 4 years once he decided not to put any more money into it.
I had to replace all the rubber hoses etc., due to dry rot from the southern climate.
I also added the Autothority two chip set up. Other than that it is stock.
Thanks Rich
Three Wheelin'
Joined: Sep 2002
Posts: 1,477
Likes: 2
From: No Turbo, No SC
Hi Curtis, OK your LH ECU is getting lonely, it will be happy to see your MAF again :-)
Curtis: Maybe take the Auto trans chips and change the RPM, fuel and timing parameters to match the GT chip set.
John: maybe I should do this !
I for one would like to be able to take full advantage of my GT cams without spending a ton of time on a dyno to sort things out. As it stands right now, I put down ~320 to the ground that I am more than happy with, but having the chips to match my GT cams in an automatic trans car would help maybe just a little without going over the edge.
Rennlist Member
Joined: Feb 2002
Posts: 7,060
Likes: 42
From: Cambridge England
Hi Rich,
Did you also replace the hoses under the inlet plenum ? The MAF is unlikely to be significantly aged at that mileage, unless the car has a history of short jouneys (say less that 10 miles).
A good starting point would be to run a diagnostic tester on it to see if there are any stored fault codes. With the tester you can also use the actuator tests to check that sub systems like the idle stabiliser valve are OK.
Have you checked manifold vacuum ? Does the car idle at the correct speed under any conditions at all ?
Hi Curtis,
Your car is slightly different to Malcolms, he has GT chips in a standard S4, whreas you appear to have GT cams and ECU chips in yours. Your car will have to retain the slightly higher GT idle speed 775rpm. But with the Auto idle speed drop when engaing "D".
Malcolm's car really needs the idle speed dropping down to the S4's normal 675, plus the idle speed drop for "D".
These special chips are on the "to do" list...
Regards
Did you also replace the hoses under the inlet plenum ? The MAF is unlikely to be significantly aged at that mileage, unless the car has a history of short jouneys (say less that 10 miles).
A good starting point would be to run a diagnostic tester on it to see if there are any stored fault codes. With the tester you can also use the actuator tests to check that sub systems like the idle stabiliser valve are OK.
Have you checked manifold vacuum ? Does the car idle at the correct speed under any conditions at all ?
Hi Curtis,
Your car is slightly different to Malcolms, he has GT chips in a standard S4, whreas you appear to have GT cams and ECU chips in yours. Your car will have to retain the slightly higher GT idle speed 775rpm. But with the Auto idle speed drop when engaing "D".
Malcolm's car really needs the idle speed dropping down to the S4's normal 675, plus the idle speed drop for "D".
These special chips are on the "to do" list...
Regards
Thread Starter
Nordschleife Master
Joined: Sep 2004
Posts: 9,429
Likes: 6
From: Not close enough to VIR.
I've been moving so I haven't had time to work on the car. I did take it on a 35-40 minute drive to a friend's house for storage work. (He has a large garage space.) The car had trouble starting. It would fire right up, then stmble and die. If I stepped on the gas, it would stumble until it got to about 1500RPMs. At that point it would roar to life. If I gently lower the revs, it would idle fine. If I just let off the accelerator, it would die. The first few times I stopped for stop signs/lights it died because I was too busy worrying about the barely functioning brakes to keep the revs up. After I got out on the open road (anybody remember driving through Floyd County going to SITM?) it started running much smoother. When catching up to another car I could put it in neutral and it'd idle just fine. The low RPM power started picking up after about 10 miles.
The friend who is keeping the car for me is a big car nut (Ford, Volvo, and Land Rover mostly). He came up with a couple ideas. He asked if I'd checked out the throttle body to see if it was gummed up (a problem he'd had on LH-jet Volvos and thought it was MAF) or if the idle air valve was non-functioning (which I believe I don't have from above posts). The other thing we both came up with was a major vacuum leak. The brake problems seem to be intermittant based on throttle usage which made us both wonder about vacuum.
It was great to get out and haul *** in my car again!
The friend who is keeping the car for me is a big car nut (Ford, Volvo, and Land Rover mostly). He came up with a couple ideas. He asked if I'd checked out the throttle body to see if it was gummed up (a problem he'd had on LH-jet Volvos and thought it was MAF) or if the idle air valve was non-functioning (which I believe I don't have from above posts). The other thing we both came up with was a major vacuum leak. The brake problems seem to be intermittant based on throttle usage which made us both wonder about vacuum.
It was great to get out and haul *** in my car again!
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Michael S. Palmer
Rennlist Member
Joined: Oct 2004
Posts: 10,717
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From: Southern Alberta, Canada
Originally Posted by John Speake
Malcolm's car really needs the idle speed dropping down to the S4's normal 675, plus the idle speed drop for "D".
These special chips are on the "to do" list...
Regards
The rebuilt MAF cured some issues while the GT chips engaged the power curve at a more usable level..........rev the thing like it was meant to be and look out
Rennlist Member
Joined: Feb 2002
Posts: 7,060
Likes: 42
From: Cambridge England
Hi Rich,
Ooops, just realised your is a 86 early 32v. I will have to refer you to other experts on these cars. Your car does have an idle valve. looks like it might be accessable.
Have a look at pages 24-204to 24-209 in the workshop manual - this shows the inlet system for your car, and the adjustments necessary to get a good idle.
Regards
Ooops, just realised your is a 86 early 32v. I will have to refer you to other experts on these cars. Your car does have an idle valve. looks like it might be accessable.
Have a look at pages 24-204to 24-209 in the workshop manual - this shows the inlet system for your car, and the adjustments necessary to get a good idle.
Regards
Thread Starter
Nordschleife Master
Joined: Sep 2004
Posts: 9,429
Likes: 6
From: Not close enough to VIR.
Vacuum leak (hose crumbled in my hands) and a bad plug/low compression seems to have been the problem. I haven't driven it since fixing, but ran it for 20 or so minutes reving the engine. The idle is a little higher and much more stable. It doesn't act at all like it will stall if letting off the throttle from higher revs.
