1988 IROC Z 5.7 TPI, sorry long I am stumped. I swear this car runs lean, it seems to be missing some power but it is a 2.77 On startup the car stumbles a little unless warm, if I give it some gas it is fine. At idle if I floor it the car almost dies and seemed to back fire through the throttle body on one or two occasions and then revs up fine. If I open the throttle slower the engine revs fine and sounds good. I tried all kinds of tests after a week or two of searching on and off the board and the only thing that changed anything was unplugging the O2 sensor, it didn't throw a code though, plus the ECM doesn't throw a code 44 for lean. If the car sits at idle for a minute or two it will smoke a blueish smoke but it doesn't smoke on startup and doesn't lose oil. It used to smoke on startup but stopped after I changed the injectors. Engine has about 20K miles on it I have tried the following: I failed emissions in January by about 20 HC, all I did was change the oil and run it hard on the interstate and it passed by 20 HC, I would have thought this meant the car is running rich No codes (there was a stored TPS code 22 but that was because I unplugged the TPS to see if running conditions changed, they did not change) I have an air fuel ratio guage, I know it is not the most accurate but it rarely goes into the green to show rich Timing is 6* BTDC CTS is new New MAF and relays for it - did the knock test at idle no change new AC Delco 17113483 EGR valve - no change, even tried plugging vacuum line to it and no change, tried plugging the port the hose to the solenoid is on and no change Distibutor and IM are 1.5 years old Champion spark plugs 1.5 years old they all show normal wear, no oil, no wetness, they have a tanish color New 22# flowmatched injectors from FIC Pulled vacuum from multiple sources and it is always 18 and steady. If I unplug a vacuum hose the car runs horrible, if I leave a port open I start to hear a ticking noise but once I put it back on it goes away MSD Cap, rotor and Summit Coil all 1.5 years old Autolite Pro wires, none are burnt, 6 months old K&N filters 1.5 years old O2 sensor is an NTK (NGK) 1.5 years old, I unplugged the O2 and no code set or stored, the hesitation seemed to stop or seriously diminish. Of course there was no top end power but throttle response did seem better TPS is set to .54 and goes to 3.96 WOT smoothly IAC has been cleaned twice and does work well I am out of ideas, the only thing I can think to do is get a new Bosch 02 sensor and plugs, but it doesn't seem like that would fix it. Please help.

Played some more tonight, started right up and idled normal, still hesitates on quick throttle from idle, easing into it is fine.

Tonight I pulled the #1 plug, is is a very light tan now.

I unplugged the MAF and it ran alot richer at idle but was undriveable past 1/4 throttle as it wanted to die.

It pulls really good but feels like there should be more. The Air/fuel guage goes lean off the scale when I floor it and then creeps back to stoich but never goes into the rich side until after I let off and then it only goes one light in.

I tried to test fuel pressure but my test guage will not screw onto the schraeder valve for some reason.

Anyone have any other ideas?

I can't help you on the issue, but what do you mean the fuel pressure gauge wont screw on? is it not -4AN? You might have to decore the schrader vavle. Good luck.

It is an actron testor, I bought the one that came with seperate fitting for throttle body cars. I have only gotten it to screw onto one TPI car and that was after I changed out the schraeder valve to an AC Delco replacement from TPIparts.net. I just ordered the Hypertech 4004. It says it is for GM vehicles. Summit showed it to be for LT1's but I am hoping it fits. I also ordered a CP9150 scan tool so I can make sure everything is ok with the car. Basically there are three issues

- hesitation off idle if I open the throttle plates all the way
- air/fuel ratio guage saing the car is lean off the scale when I floor it
- my seat of the pants feel that the car should just have more. I have only had 305 thirdgen's in the past, TBI, carb, HO carb and TP. I have had an LT1 and LS1 fourthgen and of course they were much faster. But my IROC has beat a modded VTEC Prelude and a Monte Carlo SS with a modded 350 so I guess I can't complain. I will say I would rather have a TBI 5 speed car though. TBI is so much easier to work on. Every test I have run on this car says it should run fine but it just doesn't seem right.

Ok I may be onto something now. I got my scanner and after a few hours of messing with it I got it to work. I was not able to start the car because it was too late and my son was sleeping. But I read live data anyway and it did show something interesting. The CTS in my car is only a year and a half old but it was reading 107*. It was only about 70* at the time and the IAT sensor agreed with me because it showed 70*. The car hasn't been run in days so there was no residual heat. I guess I may need to change it again. The one I had was a GP sorenson, guess I will go with AC or BWD.

One other weird thing is that the TPS showed .57 closed and when I openned it it would only go to 1.41. THe DVOM I have shows it to be correct at .54 closed and 3.96 open

And the Hypertech 4004 FP testor works great, I am getting 50 psi with the car not running.

It was the ECM. Got a new one after my scanner showed that the computer was getting the wrong readings from the TPS and CTS and now the car runs perfect.