Joined: Mar 2014

Posts: 728

Likes: 51

From: South Texas

Car: '89 Iroc Z28-15,100 Original Miles

Engine: 350 TPI

Transmission: 700R4

Axle/Gears: Limited Slip, 2.77 Ratio

I posted this on FB a couple of weeks but thought I post here to help those who might benefit from my experience. I searched this forum during the month or so that my car was down and found many posts with useful info but more times than not the OP never returned to tell how he had resolved his issue, very frustrating. Back in late December my ‘89 TPI IROC began to run very rich, surging, zero power, blowing smoke, stalling, fouling plugs and basically running like crap. The code I pulled was #45-o2 sensor rich exhaust. The rich condition was so bad that the car burned through a half tank of gas in about 15 miles. I went through two reputable mechanics that I’d used in the past but neither was able to figure out the problem with my car. I finally took it to a local shop that has been around since the early 90’s and that came well recommended by some friends. The shop was busy but agreed to take the car if I was willing to be patient. They started out by checking fuel pressure which was good, injector leak down test was good, maf sensor good, o2 sensor good, injector ohm test good. (BTW the cts sensor was replaced due to corrosion by the second mechanic and he also took apart the tank pressure valve and cleaned it) The shop also replaced the ignition module, but it didn’t remedy my problem. The shop manager finally called me one day and said he believed he had narrowed it down to the ECM and ordered an ECM for delivery. The replacement ECM turned out to be bad, so he ordered a second unit, installed it and YAHTZEE problem solved. Apparently my faulty ECM was misreading a lean condition and responding by having the injectors pump more gas. Again, I post this for those who might experience this all too common issue with our cars and so that they will look at the ECM as a possible source for their problem. The car will occationally experience a rough idle (when cold) but smooths out when it reaches operating temp. When the idle is rough the RPM will drop to around 500 and it will die unless I gun the throttle at which point it will idle smoothly again. I returned it to the shop to have that issue addressed, possibly a TPS adjustment. I’ll update once I get the car back, hopefully this week. HTH

Joined: Dec 2004

Posts: 16,900

Likes: 1,014

From: Mile High Country !!!

Car: 1967 Camaro, 91 z28

Engine: Lb9

Transmission: M20

Axle/Gears: J65 pbr on stock posi 10bolt

Joined: Dec 2004

Posts: 16,900

Likes: 1,014

From: Mile High Country !!!

Car: 1967 Camaro, 91 z28

Engine: Lb9

Transmission: M20

Axle/Gears: J65 pbr on stock posi 10bolt

Joined: Mar 2014

Posts: 728

Likes: 51

From: South Texas

Car: '89 Iroc Z28-15,100 Original Miles

Engine: 350 TPI

Transmission: 700R4

Axle/Gears: Limited Slip, 2.77 Ratio

Got her back from the shop a couple of days ago. They completed the IAC, TPS Adjustment/min air set. I picked the car up and she ran fine coming home, no issues to report. Yesterday I took her for a short drive to have the ECM relearn as mentioned in the TPS adjustment instructions, she started fine and idled steady, I drove back home and parked her. Two hours later I went out and started her, she started fine but after a few seconds the RPM dropped to about 600 and the engine shook and stumbled again as if she would turn off. I gunned the throttle and she corrected, came up in RPM and after that no issues. I checked codes and pulled a 22 -TPS error, which I assume the shop failed to clear after adjusting the TPS. I pulled the negative battery connection for 5 minutes then started her back up, she ran fine, I shut her off, no more codes. Ill check again tonight but it seems as though the idle only stumbles when I start her up after sitting warm for a couple of hours and once I hit the throttle she recovers with no further issues.