Every time I start the 98 bonny sse things seem normal for the first minute, then the engine starts bogging and rpm'* vary from 400 ish to 1100, back and forth. By the time I'm out of the driveway the pedal acts like it isn't talking to the engine. The check engine light has come on twice. Both times it says 2 codes dealing with bank 1 below threshold or efficiency low blah blah. I believe it'* code 0143 and some other one pointing to either the O2 sensor or the converter. The CEL doens't come on when the problems show up, but weeks later, then I have it checked and reset. My converter doesn't rattle and I have replaced both front and rear O2 sensors but nothing has changed. It seems like a TPS going bad or the coolant temp sensor since I notice most of the problem a few minutes after I start the car, but I noticed that even after the car is warm (200*) and is started again that the problems come back then go away after a few minutes of driving. Is this indicative of a cat converter going bad? Plus, don't those other sensors have their own code when they go bad? - I thought so. In the past when a converter went bad I could feel a definite blockage in the exhaust and power loss, plus noisy rattling; but such is not the case with this car. Like I said before, the DTC'* point me towards the cat, but I don't want to accept that. Isn't there something that I can plug in to the O2 sensor plug that tells the computer an optimal reading and makes the engine run that mixture all the time? Any help is appreciated.

Your car has a vacuum leak. it doesn't act like it when it'* cold because the computer enriches the A/F mixture for startup.

Start looking.

it does act up when it'* cold. The car isn't running for 3 minutes by the time I'm out of the drive way the engine is idling poorly and chugging and no matter what I do to the gas pedal it doesn't respond until another minute or so, then it cruises fine. If I park the car and start it again regardless of engine temp, it chugs and idles poorly then evens out a couple minutes later. I think it is my cat going bad, I just don't want to admit it - or pay for a new exhaust system which has about 105k on it. I'll look for a vacuum leak, but I know what that feels like and this isn't it.

What makes you think it'* a bad cat besides the engine codes? Is it possible those are old codes?

Usually if you gun it a bad cat will sound restricted.

I would test the MAF and look for vacuum leaks as they are simple and cheap checks.

How long has it been since you had
Plugs?
Wires?
PCV?

It'* been about 3 months since plugs and wires. Never had pvc replaced. The reason I'm suspecting the converter is because the OBD system is telling me, HEY STUPID, LOOK HERE!!! plus it'* high time to inspect/replace it since it'* original equip and has over 105K miles. If it were the MAF or the temp sensor or IAC or TPS I'd probably be seeing those codes register, but I'm not. Just those 2 about bank 1 below threshold and something efficiency low, both having to do with the O2 sensor readings off the cat. Those codes are the only ones in there and have only been showing up this month. Before then everything ran like a rolex. I'll look around for vacuum leaks, but there isn't much it could be there. I'm gonna take it to an exhaust shop and see what they say. Thanks for the feedback.

I still think it'* a vacuum leak. The richer A/F ratio provided by the computer at cold startup probably lasts right around three minutes.

In my 45 years of being a car guy, I've learned by experience that at least half the time a rough idle and running poorly at low speeds is caused by a vacuum leak.

doesn't cost anything to check out first, either.