Idle problem - part 2 (long)
Thread Starter
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
Re: Idle problem - part 2 (8388) - I think I found it!
More than likely its a vacumm leak. The sensors and the ecm always try to correct for fuel and timing, when a vacumm leak is present it tries or attempts to keep the idle at the factory settings, but eventually it loses, so it searches for a correction again. It's like setting a plane on auto pilot without having the proper air speed.
Thanks for all the great replies.
:)
[Modified by Mike263, 9:37 PM 4/11/2002]
Thread Starter
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
Re: Idle problem - part 2 (8388) - I think I found it! (Mike263)
Crap! I didn't find the problem. That vacuum leak wasn't it. Still got an erratic idle this morning in park: - 800rpm - 400rpm -800rpm - repeating. I turned on the A/C and it stablized at 600rpm after a few seconds. Turned off the A/C and it stayed stable at 600rpm. A friend suggested I change the base timing a little and see if it makes a difference - I went from 6 deg BTDC to 8 deg BTDC. Took it for a test drive (after resetting the ECM) seemed OK, but I'll need a day or two to really see.
Team Owner
Joined: Aug 2000
Posts: 24,125
Likes: 3
St. Jude Donor '14
Re: Idle problem - part 2 (Mike263)
Mike I still believe you have a vacumm leak. You mentioned in the begining of this thread the you started having the problems after the install of a new set of injectors. Check where the runners meet the plenum and the base.Check the area around the injectors. Check the hose going to the brake booster.
Pro
Joined: Dec 2000
Posts: 534
Likes: 32
From: Farmington NY
Re: Idle problem - part 2 (Mike263)
I'd say it migh be running rich, I have had the same problem and the injectors were too large. An AFPR helped but wasn't the solution until I put the correct injectors in. It still searches alittle between 600 and 630 but nothing like it did before! I'm going to try some of the other suggestions made to you to even it out. Thanks.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: Idle problem - part 2 (Mike263)
Could a bad MAF cause the surging idle problem I have? I don't have any codes thrown. Maybe the wiring to the MAF?
Don't forget about what I said about the gaskets. There a total of six gaskets for the runners, two for the top (runners to plenum) and four for the bottom (runners to intake manifold base).
A quick look and you'd think they are interchangable side to side, but two of them aren't. If you mistakenly installed these two on the wrong side of the engine you'll get a vacuum leak and bad idle.
Another source is where the injector fits into the mainfold base. There are rubber "O" rings used to seal those spots, but sometimes the "O" ring can be left off, cracked or not seated properly. Spray some injector cleaner where all 8 enter the manifold and see if there's a idle change.
Check the power brake booster vacuum fitting where it screws into the plenum at driver's side rear. Could be a small leak there.
Underside of throttle body has a vacuum port (toward driver's side); check that the hose in connected there, also the EGR vacuum hose under the plenum.
Keep us posted.
Jake
Thread Starter
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
Re: Idle problem - part 2 (JAKE)
Thanks, Jake. I removed the injectors and reinstalled checking o-rings and new runner gaskets - yeah, I see that two of the bottom gaskets are different - got them in the right place.
All vacuuum lines are connected and I replaced almost all of them - vacuum tested each line. Can't tell about the brake booster - it looks ok.
Spraying throttle body cleaner around each injector didn't make any difference - no leaks found.
I have the stock fuel pressure regulator - not adjustable. Pressures check within spec. for stock.
Another data point: I set my base idle after the reinstall of the injectors. When I cranked the car up with the IAC closed and unplugged, the erratic idle was present! So it has nothing to do with the IAC.
All vacuuum lines are connected and I replaced almost all of them - vacuum tested each line. Can't tell about the brake booster - it looks ok.
Spraying throttle body cleaner around each injector didn't make any difference - no leaks found.
I have the stock fuel pressure regulator - not adjustable. Pressures check within spec. for stock.
Another data point: I set my base idle after the reinstall of the injectors. When I cranked the car up with the IAC closed and unplugged, the erratic idle was present! So it has nothing to do with the IAC.
Drifting
Joined: Nov 2001
Posts: 1,783
Likes: 2
From: Latham NY
Re: Idle problem - part 2 (Mike263)
I suggest you look at the ignition system. Test your wires with an ohm meter. The longer the wire, the higher the resistence but they should be about the same ohms per foot. When were the cap and rotor replaced? You can have your ignition module checked at most auto stores for free. Pull the plugs to see if they all look alike. If one looks different you can narrow down the problem to that cyclinder. Keep us posted.
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Le Mans Master
Joined: Nov 1999
Posts: 8,512
Likes: 3
From: Memphis, Tn
Re: Idle problem - part 2 (Mike263)
Hey Mike. I'll pass on what I learned recently with my 85. I've been fighting an idle quality problem too. I removed the throttle body and cleaned it. There was a lot of carbon on the back side. This helped, but I still had problems. This past weekend I replaced the valve seals, springs, and rockers. Huge improvement in idle. I read a post a while back where another forum member improved his idle by replacing the valve springs. Also found that I may have a burned exhaust valve. :eek: The cylinder checks OK on compression, but when I put air in the cylinder to hold the valves up, I could hear air coming out of the exhaust pipes. :cry
Hope this helps.
Hope this helps.
Drifting
Joined: Nov 2001
Posts: 1,783
Likes: 2
From: Latham NY
Re: Idle problem - part 2 (85 Dave)
Also found that I may have a burned exhaust valve. :eek: The cylinder checks OK on compression, but when I put air in the cylinder to hold the valves up, I could hear air coming out of the exhaust pipes. :cry
Hope this helps.
Hope this helps.
Le Mans Master
Joined: Nov 1999
Posts: 8,512
Likes: 3
From: Memphis, Tn
Re: Idle problem - part 2 (Bluevette85)
This air sound is normal and doesn't indicate an exhaust valve leak if your compression test is good. I was worried about this when I used air to hold the valves up while doing my spring etc. and was told by other members that it was okay.
Thread Starter
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
Re: Idle problem - part 2 (Mike263)
Based on forum input (thanks, folks), I replaced my MAF this weekend.
I also replaced the MAF relays, to play it safe. Then I adjusted the minimum (base) idle with the new MAF.
The problem appears to have been fixed!!! WAHOO!
The old MAF (a rebuilt one about a year old) did not cause any error codes.
The biggest clue was the surging idle when the IAC was unplugged. This time (new MAF), with the IAC unplugged, I had a nice steady idle.
:)
I also replaced the MAF relays, to play it safe. Then I adjusted the minimum (base) idle with the new MAF.
The problem appears to have been fixed!!! WAHOO!
The old MAF (a rebuilt one about a year old) did not cause any error codes.
The biggest clue was the surging idle when the IAC was unplugged. This time (new MAF), with the IAC unplugged, I had a nice steady idle.
:)
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: Idle problem - part 2 (Bluevette85)
You've got to make sure that the lifters are on the base circle of the camshaft to insure they both are fully closed. Even a tiny bit open will result in compressed air getting by.
If you have doubts, remove the rocker arms completely from the suspected cylinder and make sure the piston is as close to TDC as you can estimate it.
Then, all you should hear is air escaping past the rings into the crankcase,which is normal.
If compressed air is still heard coming through the exhaust header, even with the rockers off and piston at TDC, well, you've got a leaking exhaust valve problem.
Keep us posted on what you find.
Jake
If you have doubts, remove the rocker arms completely from the suspected cylinder and make sure the piston is as close to TDC as you can estimate it.
Then, all you should hear is air escaping past the rings into the crankcase,which is normal.
If compressed air is still heard coming through the exhaust header, even with the rockers off and piston at TDC, well, you've got a leaking exhaust valve problem.
Keep us posted on what you find.
Jake
