Hey Folks, this one has me baffled. My 86 with a 22re has this miss/studder at idle and at partial throttle. I've verified TPS/Air flow meter/resistance are good. New O2 sensor. Complete swap out of ignition system. (coil/ignitor/dist./wires/plugs/dist. pickup). Now here's the really strange thing.... I turn on the AC (which kicks up the idle via a metered vacuum leak)and the miss goes away. The engine runs perfect as long as the AC is turned on. The second I turn off the AC, the misfire/studder comes right back. <img src="/forums/images/graemlins/confused.gif" alt="" /> <img src="/forums/images/graemlins/confused.gif" alt="" /> Any help would be greatly appreciated.

Welcome to the board!!

Verify that you have no air leaks, especially in the rubber connector portions around the air tube connections, between air filter housing and throttle body. The slightest of cracks there will cause issues. Also, does it run better if you turn the idle up a bit?
Hope to wheel with you soon,

Staceman

Thanks Staceman. I've got a brand new flex connection between the throttle body and the air box. The old one cracked in the 90 degree bend. I haven't adjusted the idle screw on the throttle body to make it idle faster (will adjust just to find out) but the studder/mis also occurs at partial throttle. Throttle response is dead on. No bogging or mis when quick burps of throttle are induced. Why in the world would turning on the AC make those misfires disappear?

Is the check engine light on, is it throwing any codes?

This is a long shot, but it's the only theory I could come up with...

As I understand it, the A/C idle up system works by allowing more air into the intake at idle. The only way I could see this smoothing things out is if the truck were running rich, i.e. leaking injector maybe? Can't think of a single other thing that would cause that.

May want to go through and make sure the valve adjustments are good too, although the fact that you can make it run fine with the A/C makes me doubt the problem lies there.

No codes are being thrown <img src="/forums/images/graemlins/confused.gif" alt="" />. Just finished running a can of injector cleaner recommended by a mechanic who's been working on Toyotas for 30 years. Still doing the same thing. Would out of spec fuel pressure create symptoms like this? I'm almost ready to pull the injectors and send them out for cleaning but hesitate because the mis disappears when the AC turns on.

No idea on the fuel pressure. Do you know for sure it is out of whack?

How/when did this problem crop up, anyway? Anything tweaked/replaced before it started?

Also, what kind of plugs/wires did you put in? These engines really don't like Bosch plugs, and wires other than OEM or NGK seem to be hit-or-miss.

OK, here's the whole skinny... engine is freshly rebuilt (less than 1000 miles ago). Bored.030 over, with Northwest Offroad header and LC engineering cam. LC engineering dist. and wires. Plugs are brand new OEM (I knew about the Bosch being bad) <img src="/forums/images/graemlins/smile.gif" alt="" /> I sprayed every vacuum hose fitting last night looking for leak, none were found. Adjusting the idle screw to raise the RPM's made no difference. I'm beginning to think that I might be running too lean with all of the engine mods along with the larger bored cylinders. My next step is to adjust the Air flow meter to "richen" up the fuel mixture and see if that makes a difference. Any other thoughts? <img src="/forums/images/graemlins/confused.gif" alt="" />

That helps some, two thoughts come to mind:

1) Have you double checked the hose routing on the EGR valve? I know when the dealer left the bottom hose loose on my EGR vacuum modulator (circle thingy with 3 vac connections clipped on near the EGR valve) my truck missed pretty bad.

2) If those all check out OK, try pulling the vacuum line from the EGR valve and plugging it. I've heard of certain camshafts pulling too much vacuum at idle and making the EGR open too early.

good ideas. I'll give those a try as well. Another reason I suspect it might be too lean is the sparkplugs electrodes are all still very white after @1000 miles. Usually, I'd expect they'd have a brown shade to them.

So adjusting the air flow meter counterclockwise three teeth made the engine run better but still misses at idle and partial throttle. Still baffles me as to why with the AC on, the miss all but vanishes <img src="/forums/images/graemlins/confused.gif" alt="" />