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Discussion Starter · #1 ·
I bought a beater 1991 Buick Regal with a 3800 Tuned Port Injection V6 and it's doing what I said in the title - shudders and shakes violently under load when going up hills in 3rd and 4th gear. You can feel it the most at high speed, above 45-50mph, it's more subtle below that in 3rd gear.

Also, it has a rough idle - exhaust smells like unburnt gas when the car's stopped. I replaced the oxygen sensor and the IAC, it improved the situation, but the exhaust stills reeks a bit and the engine often doesn't idle right. Even when it does, it stays up too high, around 1000rpm in drive and even at 1100 in park/neutral.

It often tries to go down to the correct 700-800rpm, but it causes excessive vibration and a more pronounced unburnt gas smell. When that happens, it usually will try to raise the RPMs to 1000, run on them for a while and then try to go back down again. It keeps doing that over and over again.

I suspect a bad MAP sensor, but apparently this engine does not have one and just uses a MAF sensor? I'm very confused, because there are many eBay listings selling a MAP sensor supposedly for this car, and yet I found 2 forum answers saying there isn't one on this engine.
I tried to find the MAP, but couldn't locate it. Does this engine have one at all?
 
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