My '88 307 -no power,poor mileage,check engine light on

[rocketman]

I have an '88 RWD Cutlass Supreme (for my son) with 108,000 miles from the orig. owner. The check engine light comes on after a few minutes and the 307 runs like it's smothered and gets about 8 miles per gallon. I have changed the oil/filter, trans. fluid/filter, changed the spark plugs, wires, cap/rotor. No change so, suspecting the cat. convertor, I yanked it and rammed it through so it's all open. Still no change. The trans is 4 spd auto (200R4?). Someone said the computer may be the problem. I plan on a performance transplant eventually but right now I need to find out the source of the poor running so it's useable for daily use. Please help. Yes I have asked the orig. owner and he said "always ran great bla bla bla" no help. I had someone check with a scanner and they couldn't get the code. I trust fellow enthusiasts more than some guy at a garage.

Chris

 

[BB Olds]

I know this sounds dumb but did you check the air filter?

 

[rocketman]

Yes, I forgot to mention that when I listed the tune-up stuff I did.

 

[joe_padavano]

Unfortunately, there are about a gazillion things it could be. You can either shotgun the solution by replacing everything (not recommended) or find a scan tool you can borrow and have plugged in while you drive. There are a number of failures that can cause an intermittent check engine light. You need to be able to watch the sensor readings while the light is on. A cheap code reader will not do this. A factory Tech1 tool or equivalent (such as the OTC Genysis or the Snap On equivalent) will allow you to read the outputs of the individual sensors while you drive. It will also allow you to monitor the mixture control solenoid, the TPS, the MAP sensor, etc. to watch for intermittents.

Also, the 307 is notorious for vac line problems. Any split or disconnected line can cause a multitude of problems.

Finally (or really, first) get a factory service manual. The troubleshooting section is invaluable. That's what got me through all the problems on my 307 when I got it.

 

[averagewhiteboy]

My 231 has all these same issues. The CEL comes on after maybe a minute or a minute and a half...

 

[pontiacgp]

did you check the O2 sensor?...I imagine you have a feedback carb and if the O2 is defective that could cause it to run rich which would give you poor fuel milage and performance...or the choke could be stuck but I don't think that gives you a check engine lite...

 

[averagewhiteboy]

Also, my GP has the high-idle issue for several minutes as well. Not just a few seconds. Like sometimes 4 minutes. lol. Would that be choke/O2?

 

[pontiacgp]

average....that would be your fast idle which is part of the choke....you might just have to lubricate fast idle..

 

[RedHotRegal]

Does yours have cruise? My old white Regal had cruise with simular problems(high idle) took awhile to figure it out but it was the cruise linkage that was binding at the carb causing it to idle high because it would hold the throttle part open.

 

[85_SS]

http://www.monte-list.nu/tech/sescodes.shtml

Checking the codes is the first step, let us know what you find 🙂