Suddenly my evo8 has decided to idle VERY rich. It starts fine cold or hot and sits around the 15afr for 10sec then drops down to 11afr and i can smell the fuel from the exhaust. If i pump the throttle it will jump back to 15afr for 10sec then drop back to 11 again. I fitted a new front o2 sensor, no help. I also quickly check the MAF connector and checked one of my intercooler hoses hadn't blown off and that all vacuum lines look right.

Any other ideas?

 

rich idle is usually a vacuum leak and rich on wot is ur boost leak. Unfortunately, visual inspection of pipes/couplers/lines/hoses doesn't cut it. Get out ur boost leak tester, which should expose the probable vac leak. Ive had vacuum leaks from completely intact hoses.

 

Check icv, that cannot be checked visually as its behind and under the tb. Two vacuum lines connect to it

 

I would clean the MAF sensor also...very common prob.

 

leak test, take off tb and remove every sensor with tb cleaner if safe on electronics.clean maf with maf cleaner. and believe it or not i would also clean cas.

 

re-checked all the vacuum lines, found one with a small split but wasnt all the way through and fixing it didn't help. I bought some maf cleaner today i will give it a try. I did 6hrs of driving this weekend and half the time the afr was good at 15afr and half the time it was 10-11afr.

 

Is your o2 cycling?

 

Is your o2 cycling?

 

what do you mean cycling?

 

cleaned the MAF with maf cleaner today, still no good any more suggestions?

 

I remembering reading a a post just like this where a guy was having the same problems as you, he had put cams in recently. It ended up being the cam sensor that's bolted on the end of one of the cams was installed 180 off. He took it off and reinstalled and the problem was fixed.

 

I haven't touched the cams.

 

Problem solved. the new 02 sensor was dead.

 

did u not get a check engine light for the bad o2 sensor?

 

Curious about this too.