eutu1984

I have checked Ohm reading on injectors hot and cold, checked for vacuum leaks, checked EGR, checked spark plugs and wires, checked timing and ignition module, checked fuel pressure, all checked good. This rough idle started about 2 months ago after a spark plug wire came off wile driving down the highway, when at a stop in gear it idles very rough to the point I have to place it in neutral. Could the ecm been damaged by running with one spark plug wire off. Any idea what else I should look at. I have no codes on the computer. this is a 1990 auto with 185K+ on it, she starts right up hot or cold. Thanks For Any Help.

Joe C

so, let me see if I got this right - the idle problem started after one of the spark plug wires came off, and you did what - ??? did you replace the single wire, repair the single wire, or what? if that's the only thing that's been done, the single wire thing, seems to me, there's your problem. there shouldn't be any ECM issue. pull that plug, inspect, and take a really good look at that spark plug wire -

eutu1984

Yes all the spark plug wires and spark plugs were replaced, it made no difference.

antfarmer2

Look again bet you have wires crossed.

eutu1984

I have double checked that the wires are in the correct order. after checking everything that I listed what else could I check. any thoughts.

Rockcrushervette

Maybe the distributer cap didn't like that if its older! Or after market? HEI'z can have small issues cracks not seen! I have had new caps that were crap! When that coil Sparks and it doesn't ground through a plug it finds a ground! Electricity is lazy! Goes the shortest distance! Another crossed wire? Something close to the cap? If you haven't yet! new cap n rotor! Run in dark of night with hood up! May find a small blue arch! Just saying bro!

antfarmer2

and check the wires again.

eutu1984

I will check the cap its not that old either so I will place the old one back on and see if it makes a difference, I checked the spark of each wire by placing the timing light on each spark plug wire and the flash from the strobe is nice and steady on each wire, also even though it idles rough the rpm is pretty steady. I did the run at night thing, it was one of the first things I checked back when the problem started.

eutu1984

I actually have DUI Livewires, they are numbered and quit hard to screw up, other than the bad idle the car runs real strong and starts up the first catch hot or cold. I have worked on a few sbc but this idle thing has me frustrated.

Rockcrushervette

Crap! This sucks! I just went through 4 failed smogs after each getting better and better that last one was high NOX! I started looking around vacuum lines and tugging car ran like crap then turns out the EGR vacuum line from silinoid was corroded then the same for fuel pressure regulator! Started looking closer so I changed all vacuum lines! Reset TB then TPS! Car has never idled better run better accelerated this fast! Might have nothing to do with your problem but never hurts to look around just saying hope it works out bro!

1984Z51auto

Problem sounds like it could be a bad plug, bad gap, fouled plug or cracked plug insulator. Any chance the plug that lost its wire got hurt when you replaced the wire?

Cliff Harris

I suggest pulling all the spark plugs and checking them out. It sure sounds like one or more are not firing.

Ratboy

Previous post suggested egr. I went through 3 or 4 in my '89. They just don't make 'em like they used to. Pull a vacuum on it and the car should stall at idle. No effect and its leaking some where or stuck partially open. That it seemed to happen when the plug wire came off might just be coincidence.

eutu1984

All the plugs are new, just replaced this weekend.

eutu1984

I pulled a vacuum on the egr, it checks out, I also blocked off the egr tube just to play it safe and that did not change my idle problem either.

eutu1984

tonight after work I will try swapping the cap, but from what I am seeing its not the ignition. I will also run another data log at it wile just idling.

Churchkey

Stock 90 injectors are prone to fail.
Suggest ohm testing the injectors when cold then hot, 14-16 ohms.

L98's tend to swallow intake gaskets, spray WD40 through supplied straw @ all mating joints. A change in rpm = failed gasket.

If issues persist suggest a compression check, @ 185K miles the valve guides could be showing signs of wear.

eutu1984

Injectors are Bosch III's, they all ohm good, already did the gasket check, compression check is on the list of things to do, vacuum is at 19 hg and steady.

eutu1984

here is a good article on checking an engine with a vacuum gauge.

http://www.gregsengine.com/using-a-vacuum-gauge.html

for anyone not familiar with it.

Mishawaka

Great read.