I have an '85 Vette with Ed Wright Chip, been running great for 2 months... now this:

For some reason, there is a stumble in acceleration. I don't just mean a hesitation, but when your in 1st gear... and you start slowing pressing the throttle...you get a bout 1/4 inch down and it feels like the car just shuts off. Then, as you keep mashing slowly... it comes alive again and throws you back in the seat. It does this in every gear... and I have noticed that sitting at idle... if I "nail" it really hard and fast... it about goes dead... or there is a hestiation before the RPM's go up. Sometimes the hesitation gets the best of it, and with the gas on the floor, the RPM's don't pick up at all... the car is just fluttering with the Throttle wide open at like 700 RPM's.
I HAVEN't been up and around every sensor on this car for the past 15 years... but I have made lots of checks. BTW, I get absolutely no computer codes. I check the Voltage in the MAF, and it reads normal all the way from .58 volts up to just over 5 volts. FP is good, and BTW, it even does the same thing if I bypass the supercharger, and I have tried 2 air flow meters, so thats not it either. There are no Error codes stored or intermitent... reads 12's everytime I check it.

What did work (temporarily)

I disconnected the battery cable for about 10 seconds... set my idle... and the TPS voltage... and I could rev up normally. I thought, HOT DANG, all it needed was reset. This actually fixed it, all was normal again - BUT, I went for a drive, and it did great up to where I turned around (bout 5 miles) and then started the same crap on the way back.

Any Ideas on what to check or what the problem might be? I really need to get this car going. I have done so much work on it lately my wife is about ready to divorce me.

 

Do you have access to a scanner? I'd check the TPS. Both for it's idle setting, and making sure it signal is not eratic.

 

Sounds like it could be doing OK til it hits closed loop. Maybe an O2 sensor? CTS sensor could go bad, but you would notice it nearly immediately and will almost always throw a code for it.

Also is your MAF on the suck side or the blown side? I have seen some less than admirable suggestions on the MAF ATI setups in their instructions. Good luck! -Matt-

 

I have been fighting this same problem for 2 years. It was very intermittent at first. Lately I have been able to do it on demand in drive under light throttle (1/4 pedal) light load. It doesnt do it when I floor it from a stop though. Yesterday I took my distributor apart and removed the axial play from the rotor. I could actually lift up on the rotor a good 1/4" while installed which would throw the timing off substanially! I had to shim the dist shaft between the gear and the housing. This seems to have helped but I am not positive if it cured the problem yet. Prior to this I could see a slight intermittent timing change at idle with the timing light.
I have done many things to get rid of this problem and found other issues which I told myself was the cause of this. Problem was still there though.
If you find the problem please post the resolution. I will do the same.
John

 

My 1990 was doing the same thing. First it would go 100 miles between ECM resets, then 50, then 30, and so on till basically it wouldn’t run.
To work on these cars today you have to HAVE the laptop and software.

Turns out the ECM was misinterpreting the TPS. When I checked the TPS with a voltage meter it was within specs, but when I looked at the TPS reading with the Moates software it read 1.25 volts at idle.

I replaced the ECM, and all ran perfect.


:chevy

 

The TPS (Throttle Position Sensor) would be the FIRST thing to check.
Heck, don't check it. Just get a new one and put it on there. They are about 12 bux if memory swerves be norectly. :) :)

Mine would throw the check engine light on intermittenly. It was like that when I bought it. I'm pretty sure several folks had tried to fix it to no avail.

I found it would not make connection sometimes when the throttle came to idle. VERY intermittent. Sometimes you could drive almost all day without it throwing a code.
It's just like the old tv/radio volumne controls that would get dirty with age as some of the carbon wears off the control element.

If yours hasn't been changed in the last few decades it definitely should be the starting point for finding this problem.
Always go from the simplest/easiest/cheapest fix to the most complex one when you're troubleshooting. It'll save you some time and money one day.