New member seeking advice

Hello Gents: Been reading a lot of posts for awhile now and just joined. I got my grandmother's 1995 Riviera. Brought it back from Missouri 2 years ago and it drove great all the way to Dallas. It only had 90K miles on it. But for the last year and a half it's been a demon. After a month it had voltage issues and would not charge the battery. After tracking down and cleaning every negative lead I could find, a new battery and new alternator and still no go, finally replaced the ignition coil and coil packs and spark plugs. That did the trick. But after a bout a week on the way home it sort of lurched on the highway, and steadily got worse with random misfires. I have an Action scanner that works great on it, and I was constantly getting low Or sensor voltage codes, random misfire codes, and lean fuel trim codes. So as of late I have replaced the PCM, EGR valve, PCV valve, MAF sensor, TPS sensor, Air Idle control sensor, Air intake sensor, and O2 sensor, fuel filter......and several vacuum hoses. All to not much avail. It had horrible acceleration, very choppy idle, and once it would get to about 40-50 mph, it'd start shaking pretty hard.......so this weekend I replaced the intake manifold and I put the new o rings and pintle and filter baskets on all the fuel injectors. That almost did the trick as it is much better now........no lights and no engine codes yet, but it still has some choppiness to it and still starts to get that shimmy at around 40-50mh......just not as violently.........and I'm plum perplexed on what to look for next.

Welcome!  I don't know the answer to your question, but I noticed the camshaft position sensor and crankshaft position sensor aren't on the list of things you replaced.  Replacing them may not help at all, but the crankshaft position sensor at least seems to have a tendancy to go out.

dekerivers1 wrote:

Hello Gents: Been reading a lot of posts for awhile now and just joined. I got my grandmother's 1995 Riviera. Brought it back from Missouri 2 years ago and it drove great all the way to Dallas. It only had 90K miles on it. But for the last year and a half it's been a demon. After a month it had voltage issues and would not charge the battery. After tracking down and cleaning every negative lead I could find, a new battery and new alternator and still no go, finally replaced the ignition coil and coil packs and spark plugs. That did the trick. But after a bout a week on the way home it sort of lurched on the highway, and steadily got worse with random misfires. I have an Action scanner that works great on it, and I was constantly getting low Or sensor voltage codes, random misfire codes, and lean fuel trim codes. So as of late I have replaced the PCM, EGR valve, PCV valve, MAF sensor, TPS sensor, Air Idle control sensor, Air intake sensor, and O2 sensor, fuel filter......and several vacuum hoses. All to not much avail. It had horrible acceleration, very choppy idle, and once it would get to about 40-50 mph, it'd start shaking pretty hard.......so this weekend I replaced the intake manifold and I put the new o rings and pintle and filter baskets on all the fuel injectors. That almost did the trick as it is much better now........no lights and no engine codes yet, but it still has some choppiness to it and still starts to get that s
himmy at around 40-50mh......just not as violently.........and I'm plum perplexed on what to look for next.

Shimmy at highway speeds could be tires/wheels. Can't tell from here.

It would not be a waste of time to remove and clean the throttle body, although that isn't likely your root cause of problems.

Get a copy of the factory service manual set. eBay usually has them, for not too much $. Like, $30 or $40.

Consider measuring the resistance of the primaries and secondaries on all your ignition coils, see if they match, and visually inspect your spark plug wires for looseness at the terminals especially on the coil terminals -- pull them off and look inside the bots.

I'd also check the catalytic converter. Driving around with a misfire will super heat it and destroy it. It may be clogged. An easy way to check for any exhaust restriction is with a vacuum gauge. A healthy 3800 will make 20" of vacuum fully warmed up in Park at idle. Rev the engine to about 1500 RPM and hold it steady at that RPM in Park. The vacuum should be at least what it was at idle and be steady. If the reading slowly begins to drop off at a steady 1500 RPM, you have an exhaust restriction. A clogged Cat will do that.

Thanks for the replies. Yes, I hadn't got to the crank and camshaft sensors yet. It always starts up fine and never starts to stall out....so I was wondering about the Cat being stopped up, as it feels like something restricted. Before I did the intake it would shimmy like mad, as if the fuel was trying to shut off and I'd have to let off the gas.....now it's just not near as bad and can press thru it. The intake gasket was a mess and part wasn't even seeded around one port. And the EGR valve when I took it out didn't even have an o ring on it or the cap. So replacing all that helped with vacuum leaks. So yes, I guess the catalytic converter will be the next thing to look at. I did the Shocks and struts and tie rods and sway link bushings last fall so all good there.