I have a really bad surging/chuggling problem, and no idea what's causing it. My car's a 91 z28, 305(supposedly rebuilt 10k miles), T5(getting worse). Recently replaced o2 sensor, ecu, dist. cap, cat, exhaust. The problem is really strong bucking/chuggling/surging, with no or very little throttle. When I give it gas, the problem disappears. Any ideas what's wrong with my car? Thanks in advance.

 

when have you checked your firing order if you have check it again making sure the order hasnt been rotated a post in ether direction

 

Thanks, but that's not it. I just went out and checked it, everything's fine there.

 

did you replace those components to solve the problem or did this start happening after you replaced those components

also check for a vaccum leak

 

Does the car only buck on you when you are letting off the accelerator, or does it also buck when you are giving it steady gas, then you have to give it more gas to make it stop acting funny? Does the car idle funny too at a stop sign? Lastly, does the car start doing this right off the bat, or does it do it after warm up?

 

Parts were replaced for other reasons- #2 fuel injector shorted, which fried the ECU. ECU was replaced, but prom wasn't. Distributer was old and needed to be replaced. Cat and exhaust were ruined, needed replacement. O2 sensor was replaced to try to fix this problem. I don't think I have a vacuum leak.

the car bucks in all rpm ranges, at the same frequency no matter what the rpm is. It bucks at no gas and also at with just a little steady gas. Idle is not great, sometimes its solid, sometimes it fluctuates by about 100 rpm. It happens both cold and warm.

I also have a clunking noise when engine braking, probably from a worn main bearing.

 

well where to start is going to be the problem have you checked your timing after installing the new dist?
how do you know the prom is still good after "fried" ECU?
you have done a few different things that could have affected so many systems at this point it could be anything

 

Haven't checked timing, will do today. Mechanic installed both the dist. and the ecu, so I trusted that he checked timing and the prom before reinstalling it.

I'm not 100% sure, but I think the problem started after the same mechanic replaced my clutch master cylinder, but I don't see how that could be the cause of my problem.

 

when it starts surging and what not are you in neutral or does it only do it in gear?

 

Your problem is similar to one I had. I had replaced the MAF with no change. Someone on here suggested the TPS, I replaced that and the problem was cured. Just check it with a meter and you will know in a few minutes if that is the issue.

 

tps checked and good (borrowed my mechanics aldl scanner, and checked physically whit voltmeter twice)

timing doesn't make sense, because the problem is intermittent some days its bad, sometimes no even there, I also don't know how to check?

Could MAF cause this? If so how do I check it?
Also I'm running 93 octane could that somehow cause this? Should I drop to 89 or 87?
Any other ideas what's causing it?
I also get terrible gas milage, 10-12 mpg from a stock 305

Thanks for the help but I'm still stumped.