1995 Riviera SC Questions

Hello,

I have a 1995 Riviera Supercharged with 109900 Mi on the engine. I'm having issues with acceleration power. The car seems to drag when giving it gas, and when on the freeway will tremble somewhat at around 55mph, resisting further speed increase for a few seconds before accelerating further. Also, my gas mileage is terrible. I'm averaging around 12-15mpg.

So far I've replaced the head gaskets, supercharger gasket + coupler, lower intake manifold gasket, spark plugs, egr valve, and water pump. Any ideas on what the issues present may be?

Thank you

Put a scanner on it and read codes. Then use live data to monitor sensors, this will take some time to understand what is normal and what is not. It is probably OBD1 and you may not have comprehensive live data to look at without special scanner.

Typically on a 3800, it is almost certainly plug wires or weak coil pack. If it is rough at idle, you might catch it misfiring by using an inline spark tester on each plug wire at the coil packs. If not missing at idle, replace all plug wires and recheck on highway.

Those plug wires have been in a hot confined space for almost 20 years. That was my first thought.

Bernie

If you do not have a check engine light on, I would test the coil packs and replace the wires. If that does not solve your problem, I would then check the Throttle Position Sensor and cross reference the values on the scan tool with factory specs. I have seen TPS sensors go bad without setting codes and can cause hesitation and poor mileage, the exact condition you describe.

Hello,

Thanks for the responses. I replaced the plug wires, and am noticing that the rough idle is spontaneous, and sometimes the RPM's rev up to 1500-2000 with no prompting. When the engine is running rough, with each shake of the vehicle, the interior power dims a bit. It's really gotten rough lately. Definitely something electrical! I'm looking into the TPS now.. Any other possibilities?

Thanks again!

Since your interior lights are dimming, that indicates a loose connection on the battery cables

at the battery posts. a loose ground at the battery can cause all sorts of electrical problems. check to

see if the cables are tight at the bat posts. You should not be able to rotate them.I get GM cars in my shop about every two months with all sorts of driveability and weird electrical problems that all it is is a loose ground cable on the battery.

Hello,

Thanks for the responses. I replaced the plug wires, and am noticing that the rough idle is spontaneous, and sometimes the RPM's rev up to 1500-2000 with no prompting. When the engine is running rough, with each shake of the vehicle, the interior power dims a bit. It's really gotten rough lately. Definitely something electrical! I'm looking into the TPS now.. Any other possibilities?

Thanks again!

If the engine is surging at idle and the RPM is dipping low enough the alternator output will drop and the lights will dim. This is not abnormal IF the rpm is dropping low enough.

A hunting idle RPM as you describe can be a vacuum leak and should be setting some sort of lean codes. Are there any codes?

Tom Mooney

Hey everyone! Just an update. I've replaced the TPS and it's doing better there...

There is however a repeating issue of the lower intake manifold gasket leaking a little coolant.. Is this common?? I believe it to be contributing to sporadic idle RPM.