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My rough, lurching idle is driving me crazy. I have replaced the plug wires, (Borg-Warner) distributer cap, rotor, pcv valve and air filter. I put some cheap plug wires on and it got so bad the car would die. The Borg-Warner wires at least keep the idle from falling so much that it dies. I only have this problem after it warms up.

My next hope is the coolant temp sensor. This seems to be mentioned a lot as a possible cause for the surging idle problem.

NAPA guy says it sounds like a vacuum leak. I am at a loss. The surging really gets on your nerves.

Can anyone suggest an order of things to check?

Same situation with me. You should also check your TPS. I did but that was not the cause.

Does your idle fluctuate up and down or does it just drop really low? If it fluctuates, NAPA man may be right with a vacuum leak. If it dips down really low try adjusting your idle THE PROPER WAY. Plenty of write-ups (Tunes did a great one, look in the FAQ), make sure you read and follow directions, otherwise you can and probably will make the TPS worse. Connecting 10 to GRND is crucial. Again, read the faq on adjusting your tps by tunes. It helped my wacky idle anyways. Might help more if you replace the hoses anyways. I would replace mine but I'm getting a Diamante soon to replace my MX3.

The fluctuating idle problem completely stops after adding a bottle of fuel injector cleaner. Idle is smooth as silk until the next fill-up. Then the jumping high/low idle returns. Until I add another bottle of fuel injector cleaner and I am running good until the next fill-up.

Maybe you need new fuel injectors...

But if the fuel injectors were bad, it seems they would stay bad? How could the cleaner alone make such a big difference?

Try replacing the fuel filters .... might be clogged and the injector cleaner cleans the clog temporarily .....

Filter(s) More than one? Where are they located?

I think there is one near the fuel pump and one under the hood. I dont know much about the fuel pump strainer - but the one under the hood is a pain to change

I think there is a picture in this thread

http://www.mx-3.com/phpbb2/viewtopic.ph ... uel+filter

My engine is a 1.6L DOHC - i dont know if the fuel filter placement is the same for other models. You can probably confirm it in the online manual

It was the fuel filter!!!! I changed it Sunday night. Man-oh-man what a difference! And yes, it was a pain to change. I thought I would never get it done it took me so long. Well worth the effort though.

jackiel wrote:It was the fuel pump!!!! I changed it Sunday night. Man-oh-man what a difference! And yes, it was a pain to change. I thought I would never get it done it took me so long. Well worth the effort though.

Do you mean fuel filter? I thought fuel pump is relatively easy to change than the filter under the hood... Anyway if the filter was clogged - then there is a good chance of lot of sludge in fuel tank and possibly affecting the fuel pump. I am in the same situation and i am thinking of getting a new tank from ebay.

Yes, I meant the fuel filter. Sorry for the mistake and thanks for pointing that out.