My car is kinda rough at idle...and stumbles bad when I give it gas while driving?

Question

Its a 1994 Pontiac Trans Am 25th-v8 special. I accidently put bad gas in it and ran on it for a couple miles. Realizing what i did I flushed my tank. (nothing nasty was in it). I have replaced the fuel pump, fuel filter, fuel injectors, distributor, spark plug wires, spark plugs, air filter. No kinked gas lines, cant find a vacuum leak. No antifreeze is missing or in my oil. What can it be??

Answer 1

I don't have an answer but I have the same exact problem with my car, same year, V8. Stumbles really bad when I give it gas and runs better when I let up a little, still accelerating, if that makes any sense. It also idles really rough, high, then low. Makes me look like an idiot at the stop light. I just bought the car and would really like to figure this out. I've replaced plugs, wires, fuel filter, cleaned the injectors, checked all lines, etc...... I've had a few mechanics look at it and one seems to think it's some contacts or something in the distributor, but I'm kind of tired of tearing the damn thing apart trying to figure this out. Would love to find the person who can tell me exactly what it is and I'm sure the person with the same question would too, haha. I have a feeling I'm replacing everything and it's something much simpler than that. Thanks for any and all the info!!

Answer 2

this could be a number of things to be honest.. im a tech at firestone complete auto care, so we work on a variety of cars..you said you already checked for a vaccum leak which is fine if you dont have one.. you need to check all your lines for cracks and things of that sort..it could also be your m.a.f. sensor too, sometimes those go bad or get dirty.. try cleaning it. you can use carb and choke or fuel injection cleaner on it just dont power blast the thin piece of metal in it or it will ruin the sensor.. Tps could be a point too, maybe its not sensing where your throttle is located.... other than that the only thing i can think of is possibly a fuel regulator..could be sending more or less fuel to the cylinder when you hit the gas causing it either to choke out or run really rich.. air/ fuel mixture problem.. ignition wires or several other things others have said are true.. not sure about the crankshaft one.. if you had a bent crankshaft you would have possibly had a rod knock or bent one of the main seals causing an oil leak... and might have a hell of a vibration if its bent bad enough..but either way sounds like its not getting enough air or fuel when you jump on it

Answer 3

Well I know from my friend who knows his car very well. It may be that as old as your car is, the crankshaft might be bent, damaged, etc. Or, even worse is that if your car runs under 1000 rpm (1 at tachometer) the slower idling is slow enough for you to feel it. This isn't a problem, just get the idle adjusted if possible. This vibration can shake parts and loosen screws, anything like that. However, there is an even more worse possibility. The engine piston(s) might be bent, causing the piston to strike the casing inside each cylinder. However unlikely this is, it may be quite possible especially because it is not visible, and because of the car's age. I highly recommend that an authorized shop do an analyzation of your car. If he can't find anything, then it might be inside the engine or other parts that he or she cannot access. If the predicament is that the piston, transmission, crankshaft, etc, then you might want to buy a new car, as overhauling or repairing this kind of situation will cost several hundred, if not thousands. Just my honest opinion.

Answer 4

I suggest you check the EGR valve. It only opens the EGR valve under acceleration. The EGR is operated by vacuum. When it goes bad, many times the diaphragm will leak vacuum causing a stumble under acceleration. Also, you'll get some preigniton knock because your engine won't be getting any EGR when needed.

If you have a vacuum pump available from auto parts stores, you can check the operation of your EGR valve. The instructions that come with most vacuum pumps usually describe the procedure.

Hope that helps

Answer 5

If an event has occurred that violated engine management protocol, your engine sensors reported it to your engine computer, and you saw your check or service engine lamp illuminate. You need to retrieve malfunction codes using an OBDS ( On Board Diagnostic System) scanner ~ $150.00, or pay someone who has one to do it for you.
Because of strict fuel delivery procedures, rarely does anyone pump contaminated fuel anymore, so I would not blame it on that offhand. More than likely it was a non-related, coincidental engine management event. It appears you've done a thorough job checking. Do the scan. These scanners fit all 1994 and later cars, so you can use it any on car on the road across all manufacturers product lines. Money well spent.

Answer 6

It's an old car, maybe the timing is off. Another thing you can try is when starting have the starter motor on a teeny-bit longer. Sometimes, having that moment too short can cause "power issues" or timing issues.

With all those things you changed, it really shouldn't be related with fuel anymore.

Have you had a shop look at it at all? How are the drive belts? Try a machine flush

Answer 7

did you examine the air clear out? if that is obstructed adequate, it may bring about unfavorable idling and absence of means. replace the spark plugs too, think ofyou've got a nasty spark plug it truly is causing a misfire. except that, you would possibly want to bypass deeper into the motor. might want to be a nasty timing belt or some plugged gas injectors. try utilising some gas injector cleanser once you've about a a million/4 to at least a million/8 tank of gas left and run it until eventually you're almost empty so as that the cleanser is fairly concentrated. very few options before you've a professional seem at it.

Answer 8

You don't really give enough to go on......I'd check compression on all cyl, fuel pressure, engine vacuum, and spark. If all checks out then lean towards tp sensor, map sensor, etc. Poor fuel could have damaged converter, but vacuum test will confirm or deny that. Most fuel injected cars of that year have a vacuum controlled fuel rail pressure regulator, be sure to check fuel pressure while revving engine, if it doesn't increase with vacuum loss, that may be part of the problem....

Answer 9

if your car ran good before u put bad fuel in it...I would recommend you check that you got the plug wires on right ...getting two of them wrong could cause your problem..i would also buy new plugs and replace them again as they are not firing right they will be bad

Answer 10

By bad gas what do you mean? Dirty? Wrong Kind?
Their is another thing that comes to mind, can you trust the person/garage who claimed to have done all that. It seems to me that doing all that work before diagnosing the problem is someone trying to rip you off.
Otherwise try a compression test.