Recently I have been experiencing a random issue for my 93.

my tachometer randomly starts bouncing, then it also starts backfiring when increasing rpm’s,

first time it happened a couple weeks ago, car had been running good, then that evening I was in a drive thru line that was slow. While idling in gear the car started surging, tachometer started bouncing sporadically. I got to work , a bit later I went out there and noticed the negative battery cable was loose ( I had disconnected it earlier that week to move the ecu to replace the brake booster. I tightened it up, started it and it ran fine.

until last night!!!! Drove it a good 30 minutes, stopped at a drive thru to grab a bite ti eat, while idling there for a bit, same thing happened as above. This morning I got in it, drove to work and all was fine. When I got there, I sat In The car for about 15 mins in gear idling, it happened again.

work was slow today so I was able to pull it in the shop and check all the ground points. I did find that the ground strap from under the battery to the bell housing was loose. I took all the ground points loose, cleaned them and re assembled. So I started the car and it ran fine, drove it a bit and when I got back to the shop, I idled it in gear for about ten minutes and it started surging and the tech bouncing sporadically and the car would backfire.

no diagnostic codes
car Does get up to 204 while idling and I hear the fans kick on, but I did notice that it acts up around the 200 temp.

Hasn’t acted up when driving, only sitting in a drive thru idling, or idling at the shop in gear.

Opti is 6mos new
coil pak 6mos new
iac 6 months new, heat/thermo grease applied to both
Also replaced MAP sensor 6 months ago

any ideas

 

Many years ago when my 94 was new to me, I experienced this problem in the first week of owning it. It was the ignition control module failing under heat soak. It is located standing off the front facing side of passenger cylinder head. It was fine till things had time to get toasty.

The missing tach signal coinciding with the skip in the engine. And a bounce in the tach. Something to think about. Parts stores may test it for you but if it is failing under high heat conditions only they won’t duplicate it.

Maybe your problem, maybe not. Worth looking into further.

 

Thanks for the feed back. It is fairly new but bought at Oriellys. I may just remove it and they will warranty it for me. See if that works!


if the ignition control module was bad, would t it throw a diagnostic code?

 

It may, it may not. I wouldn’t be surprised if it was bad, the aftermarket overseas components in my experience are failure prone junk compared to the OEM equipment. Where they might try to get you is if they bench test and it checks out. You’d need to blast it with a hair dryer for 10 minutes first to have it see the same heat it sees on car. It lives an inch off the cylinder head with 200F air from the fans blasting it.

What brand Opti did you put in it? Lots of junk out there for those too. I’d say MOSTLY junk out there in fact with a few reputable exceptions.

 

When you replace your icm, be sure to clean the aluminum heat sink and apply fresh thermal grease to the back of the new icm before attaching it to the heat sink. I had issues years back in my 94 that were similar, and it ended up being the aftermarket icm that was causing some of the issues.

 

I’m going to replace the ignition control module. Sounds like that is most likely what it might be based on y’all’s feedback. We deal with Oriellys regularly and they don’t even question/hassle us with warranty parts. I give them the old and they give me the new.

I will let you know the results!


I have a petris opti

 

Replace ignition control module and all is well

 

Glad to hear that it fixed your issue!! Did you install new thermal grease on the back of the new icm before mounting it to the heat sync?

 

Yes I did, u could tell that previous owner did not.

 

Good work! Not having the thermal grease on the back of the icm can cause it to fail quicker due to the lack of heat dispersion to the heat sync and can cause it to overheat and fail quicker than it normally would.