Olds 4.0 1998 ideling very rough and mpg way down changed fuel filter and run some injector cleaner and no diffrence just over 100 thou. Wifes HIGH TEST GUZZLER 93 oct.:mad: darn race car...........
Any thoughts or quick tests before we take it to a $$$ taker ??
It ran fine till a month ago
when sitting warm at a stop light it will surge from about 500 rpms/800 and sound like a klunk or knock and when put the pedal down full just ugly(feels like not getting any fuel) till a second or two later she'll smooth out and run a bit better put not like a month ago............????? thanks:(

How rough is very rough? Could it be a miss? If that car runs on coil-on-plug setups you could have a bad coil.

The hunting for idle and bog sounds like it could be a vacuum leak, as well.

Pull the vacuum line off the fuel pressure regulator and see if it's leaking fuel.

Vernon

Rough is ....idol -idol -surge- knock- idol- idol-- idol--surge -surge knock....When you go to power brake it starts to growl and rumble like a starved lion of fuel then when let go,it catch'es up and goes??? I took the MAF out and cleaned (brake cleaner) same thing, air filter looks about half.

Check the fuel pressure and let us know what it is. If it is low, you probably need a fuel pump or regulator.

Ck it out seems to have some, no gauge but sucks your finger real good.It surge and klunks with vacum on and off the regulater.
Today try the power brake again and it boogs down real Baad and grumbls and shakes
The good vacum is in the hose not the regulater ...should there be a vacum outta the REG if so there is none..............
Ps ..what should this car run temp wise it seems awefull hot 220 wife says she thinks it always runs that hot testing the other day was even higher