rullywowr

2000 5SPD Max:

Had a rough idle, did a tune up and found that some idiot mechanic replaced the front 3 plugs with Autolites but the back three were OEM NGK. The gap was so big that my gap gauge wouldn't even read them Also #6 coil was loose from that same idiot not tightening the screw on the coil pack.

So I figured I would clean the TB to improve performance. I cleaned it as it was really dirty, replaced the proper two gaskets (o ring and TB black plate gasket) and put it back. Wham...instant high idle (around 1500) and no amount of IACV relearn would help.

Fearing the worst I took off the TB numerous times and checked for any vac leaks, changed the PCV, bought a new IACV, set the TPS with feeler gauge and backprobes (changed out the phillips to hex head) did the relearn and still it would idle way high. The car would also throw a pending P0505 and then a solid P0505 error as the IACV couldn't compensate.

I feared the worst and pulled the ECU twice (also replaced those screws with hex head...what a PITA). After examining the STA508 chip it was fine. The ECU looked mint, no issues no burned traces.

So after putting it back for the millionth time I looked carefully at the idle screw you are not supposed to touch. It looked to me that the red locking paint was not in the same position on the locking nut....after exhausting every other possibility I carefully adjusted the idle nut and backed it down until the engine would idle around 675 RPM. Of course after doing so you need to adjust the TPS so the open/closed switch is in spec with the feeler so the open/closed switch works properly.

All is good! Idles like a champ, has lots of power, runs strong, and life is great. I am assuming that the idiot mechanic that worked on this car previously upped the idle screw probably due to it idleing like crap (as a result of the TB being carboned up and the 3 back plugs being WAY past worn).

I feared the worst (ECU)...but simply going through all the steps the idle screw was the last possible thing it could be. I am writing this in the hopes that it may help someone in the same position (cleaned TB, changed IACV, good ECU and still high idle)...of course make sure all your other prerequisites are in place before just going straight for the idle screw.

Amerikaner83

iTrader: (17)

Nicely done on the troubleshooting, my friend

Gemner

iTrader: (4)

the old plugs had a huge gap or the newly replaced plugs did?

rullywowr

All the plugs needed replacing but the ones in the rear bank were original NGK and had the HUGE gap from wear...we are talking like way in excess of .080 They were almost worn down to the insulator! Couldn't believe it was still running.