Hi Guy's,

Hope you can help. I have a 91 RS with 305/700R4. The car has an erratic idle when the car is in drive and I have my foot on the brake when I'm stationery. It only happens after I have been driving it for about 10 minutes. The idle will go up and down,sometimes it will stall. If I shift the car into neutral the idle evens out and its ok.

Any suggestions as its becoming a pain at lights and junctions etc.

Thanks,

Alex

 

When was the last time the car had a good tune up? Check for vacuum leaks around the base of the TBI unit as well as all lines that attach to the unit. Change your fuel filter and 02 sensor. From there you may want to change your plugs, wires, cap and rotor. It sounds like a bad 02 and or a small vacuum leak is causing your problem.

 

Thanks will do that. I don't think it has had a tune up in a while. It has had new plugs,wires,distributor and ignition module. The previous owner did that work as I have all the old parts he replaced.

Car doesn't have any hesitation when you step on the go pedal.

Alex

 

I think theres a vacumn hose connected to the brake servo from the throttle body check there for leaks..
your timing may be to low..like the car can't handle the extra demand of the brakes pulling against the force of the tranny in drive...
Also dissconect the battery and trying cleaning the IAC valve..

it's going to be crud or a spilt pipe I think..

just my 2 cents

 

Hi Guy's,

I checked the car over yesterday. Took the filter housing off. Had a good look around, car looks like it had a recent tune up. New IAC valve,Oxygen sensor,air filter,plugs,ignition cap.

Found one small hose that looked suspect so changed that. Also the igntion cap was not secured at all on one side. Tightened it all down and ran the engine for 30 minutes.

It looks like it might have cured it. Have to take it out on a run today to find out.

Alex

 

No way it was that little bolt
Excellent. glad to hear you fixed it.

 

Hi Guy's,

The problem is back again. It took longer to appear this time. I'll take the IAC valve out and clean it see if that works. The valve looks new to me though.

Alex

 

Don't take it out, try unplugging it and see what it does.

 

Hi,

I unplugged the IAC when it started happening and the revs shot up but no erratic idle. I took the IAC valve out and cleaned it and used carb cleaner on the passageway. The valve did not have many deposits on it. The valve has been replaced recently by the looks of it as it still looks new.

Any other suggestions? The only other thing that has been changed lately is the EGR valve.

Thanks,

Alex

 

Try setting the minimum idle speed, there's a writeup on how to do it in the Technical Articles on the site.

 

Hi,
Minimum Idle speed was fine. I checked that out Sunday. Went to start the car today and it took ages. Had to keep my foot on the gas then it idled ok.

Took it out for a drive and all seemed to work perfectly, shut it off for a couple of hours then when I went to start it had to keep my foot on the gas again.This time when I took it for a drive I had to left foot brake and keep my foot on the gas to keep it running.

I checked for vacumn leaks again and changed one small pipe that had a crack in it.

Any other suggestions?? Its driving me mad.

Alex

 

It was mentioned earlier, but did you ever change the fuel filter? Or happen to check fuel pressure?

 

I second this as well.

 

Hi,

Will check that. It did seem like no fuel was getting through or low fuel preasure. I also have another TBI unit coming which I was going to swap first. The new TBI is off of a working car.

Thanks,

Alex

 

I'ld put my bet on ignition problems still (coil/distributor). Seems to coincidental that the problem was partially "cured" when he messed with the ignition cap. I'm wondering if it caused a latent problem elsewhere. Checking Fuel problems is easy and cheap, after that, I'ld go back and look at the electrical.

 

Hi Guys,

Ok I have now replaced all the ignition leads,plugs,cap and rotor,PCV,fuel filter. Car is running now but has a lope with the revs going up and down and then it may stall. Still stalls if I have it in drive with my foot on the brake.

Any ideas?

Thanks,

Alex

 

Just curious, but when you changed the cap and rotor, how did you put the spark plugs wires back on? Did you swap them one by one, or yank them all off and go by the firing order? The loping idle sounds like it might be a misfire. I would highly suggest double-checking the firing order, it's easy to get it wrong (happens to me all the time ). Have you checked the timing?

Here's a picture of how it should be:

5.0L and 5.7L Engines - Engine firing order: 1-8-4-3-6-5-7-2 - Distributor Rotation: Clockwise

 

Hi,
No checked all of that. Took the wires off one at a time. Car runs fine otherwise.

Thanks,

Alex

 

well i hope you let us know what it was once you've diagnosed the problem, I'm curious to know what it is...seems like you've done a lot of things that haven't solved the problem yet

 

Good, just wanted to make sure.

At the moment, the only suggestions I have are timing and fuel pressure. I'm going to check out my service manual tonight and see if I've forgotten any possible causes for a bad idle.

 

Hi,

I'm going to get a spare set of sensors and change out each one just in case. Its annoying I know.

Alex

 

ITS FIXED!!!!!!


Hi Guy's,

Thanks to all those who put suggestions forward. Now have it running perfectly. In the end it was a vacumm leak by the looks of things. I started playing around with the M.A.P sensor and when I went to remove the vacumm line it didn't seem to be on tight. I think with the engine warm it was enough to expand the rubber.

So I went down to autozone and got some vacumm line and various rubber elbows. I replaced any that didn't seem tight and behold no more missing or stalling. Total cost of the fix $8.

But the car now has a full Holley ignition system with High performance coil and Annihilator igniton module. High performance cap/rotor and ignition wires.New plugs,fuel filter,air filter. Oh well won't need to change them for a while.

Also fixed my air conditioning yesterday as well.

So far its a good week.

Alex