Help - muffled thumping in Cutlass 307, 54k orig miles

[jamesejam]

I just bought a 1987 Cutlass with a 307 and 54,000 original miles from a 92-year-old lady with all receipts to prove that she meticulously took care of it. The car runs fine (although slower than my 3.1L Ciera) but there's a real mild thumping feel when I'm at idle. It doesn't thump exactly in time with the engine, only about once a second, and it's pretty mild but noticeable if you're paying attention. Is this just what the engine feels like? It seems to run/sound totally normal when I open the hood and listen, but I can feel it when I'm in the car. Could it be - fouled plug from only being driven once a week? Bad harmonic balancer? Spun bearing? Something else?

 

[kustomkyle]

My 1986 Buick Regal with the exact same engine does the same thing, I believe. Is it like a random "boom...boom-boom..........boom"? If so, it's probably the engine missing. My car sat for a year in someones yard with low, bad (black) oil in it and then started without any precautions or preparation. This, I believe, caused a number of issues, and it now burns a lot of oil/misses at idle.

I don't know much of anything about engines, but if it is that your car is missing, but doesn't put out smoke (especially blue), it could be a fairly simple fix. But finding the exact culprit can be a challenge. It could be a cracked vaccum line or lines, the EGR valve, or some other emissions related item. It could also be a spark plug/plug wire issue.

 

[dan2286]

Pull the inspection cover off of the trans and make sure the torque converter/flexplate is tight.

 

[smoknum]

olds 307

it could be the exhaust hitting the floor of the car

 

[jamesejam]

It does this regardless of whether the car is in Park or in gear.

 

[Doober]

I'm with smokum, it could just be something simple as a loose exhaust. It could also be a minor miss though... when was the last tune up on the car?

 

[pokertramp]

Look for a bad plug or wire too or something in the ignition system.

 

[jamesejam]

FIXED IT - replaced the flex plate (paid a mechanic $900 for this and a new transmission filter and fluid. It still shook, just not as bad. Mechanic said "it's an old car, they do that somewhat." Then, on a whim I looked at the belts while the car was running - saw my Air Cond belt was partially torn...took the whole unit off and now the shake is gone! But one of my other belts is slipping now...

 

[85 Cutlass Brougham]

Why take the A/C off? Wouldn't it have been better just to change the belts?

 

[DelOhio]

Why take the A/C off? Wouldn't it have been better just to change the belts?

Especially liveing in Cali! Its hot year round out there. Hope you'r windows go down.