Help !! 99 3.5L Random Multiple Misfire

Just wanted to know if anyone had any advice on where to start looking for the root of our random multiple mis. The car has poor gas milage, new plugs, new fuel filter, new air filter, cleaned throttle body, and sensors and still have multiple mis. Codes that come up are random multiple, maf sensor read high or low, no intake leaks detected. If anyone can help guide us in the right direction that would be wonderful !!!

Clean battery cables of corrosion, pull back the boots even to make sure there is no corrosion.

Check the fuel pressure, exact figures escape me, but it should spike into the 40s IIRC when you first turn the pump on, and fall back into the 30s when running.

You might also try some water removal solution in the gas.

Are you saying that you are getting a MAF code too?

Try cleaning the MAF as well. Use carbuerator cleaner or the like and very carefully clean it with a soft rag.

Thanks for the help guys but .... it is as simple as a goofed up TPS!! Figured it out this morning. Thanks anyways.:grinno:

Excuse my car ignorance, but what is a TPS? I ask because my 1999 3.5 has also been getting poor mileage and I've done lots to try to resolve it, to no avail (I've posted about it in the past). I don't get any lights but my mileage basically went from solid 19/20mpg down to 14/15 (all suburban driving) pretty much overnight.

Also, can anyone tell me where the MAF sensor is located? The intake hose I guess, but whereabouts in it?

Thanks!

Excuse my car ignorance, but what is a TPS? I ask because my 1999 3.5 has also been getting poor mileage and I've done lots to try to resolve it, to no avail (I've posted about it in the past). I don't get any lights but my mileage basically went from solid 19/20mpg down to 14/15 (all suburban driving) pretty much overnight.

Also, can anyone tell me where the MAF sensor is located? The intake hose I guess, but whereabouts in it?

Thanks!

TPS is the Throttle Position Sensor, its atached to the throttle body and sends information regarding the position of the throttle plate to the PCM.

Youre on the right track, the "thingy" in the intake hose is the MAF housing, the actually sensor is inside the housing, you have to take off 4 Torx screws to view/clean it etc.

As for your mileage, have you changed the O2 sensor? I cant remember from your posts if you changed it or not.

Hey hoov, thanks. Yes, so far I've done new GM platinum plugs, O2 sensor (I found out the 'walker' brand sensor is a repackaged 'denso' sensor btw), a $180 fuel system cleaning at a local pontiac dealer, minor stuff like tire rotate/balance, some chevron techron and more recent a marvel mystery oil gas treatment (still 3/4 tank of that left actually, but I'm not expecting anything from it). About a month ago I took it to the Oldsmobile dealer and they couldn't find anything wrong either.

I don't know how much they checked out. The guy on the phone said they could do some diagnostics (folks on the 'net said they can check stuff while the car's running), but when I brought it in the mechanic seemed to have the 'tude that with no CE light they can't do much. I waited about 30-40 minutes while they looked at it, but I'm not sure what they checked, at least they didn't try to charge me anything though.

I've been meaning to get in touch with a good mechanic I saw for the first time since high school at a funeral a couple years back. 2 GM dealers (one being an Olds dealer) haven't been able to find squat so I plan to relay the suggestions here and from other forums to him. I'll check out the MAF sensor but I donno what or where the TPS is or how I'd know if it was working right. I guess since I get no lights it's probably okay.

BTW, hope you don't mind me hijacking your thread a bit there, littlestachon. I figure it's cool since you found the fix, right?

Something else you may want to try that is an inexpensive fix and worked with ours is changing the spark plug boots. They are small rubber tubes that connect your spark plug and your coil and they conduct your spark. If those are cracked or stretched in any way they will not fire right causing the random multiple cylinder miss. I got mine at a GM dealer in Canada and they cost me $9.00 a piece and helped with the problem. It is alot cheaper than starting to pay for diagnostics on a problem that isn't offering any codes. Hopefully that is helpful

I have same year and engine with the same misfire problem. It turned out to be a bad MAF sensor the cars flys after replacing it.

ACTUALLTY, it has turned out to be far worse of a problem than a sensor, the electonic pressure control solenoid is finished in the transmission. It is a 90$ part but a $500 fix!!! This will rectify all problems with this stupid car!!! Thanks for the attempts to help though.