I need help diagnosing a high idle and pinging engine problem.

I had a high/low/high idle problem and replaced the TPS and IAC bypass valve. The rough idle and up/down idle were cured but now its just higher than normal...

The high idle is only slighly up there, 1200 rpms at idle and in neutral, but its enough to move the truck and is definetly not the norm. I am also getting pinging at all rpms over 3000, especially under a load. I recently replaced the sparkplugs, wires, rotor and cap, coil, and added an msd box also. The ping was there beforehand and I thought it was a timing issue. I reset the timing to 10 btdc. When I pulled the plugs the insulators were bright white and chalky indicating a lean condition. The pinging engine sounds like quarters rattingling around inside....for lack of a better description. The ping has been there for some time but was only noticable at 4000rpm, now its much worse....also, i've developed a tapping that seems to be in the valve area. Have I done any damage?? What should I look forward to in repairs in the future for letting the detonation go on so long. Compression check shows 150-160 psi on all cylinders. 1994 F150 4x4 with 125k miles running 89 octane fuel.

These error codes that I dumped from my ecu are:

212 in KOEO test
loss of ignition diagnostic monitor input to pcm/spout circuit grounded

411 in KOER test
cannot control low rpm in KOER test

I also pulled off the IAC connector while the truck was running and it just kept on going the rpms only dropped slightly, i thought it was supposed to die eventually. The TPS and IAC are both new and recently replaced. If I didnt calibrate the TPS would this cause the 411 code or do I have a vacume leak somewhere?? Blocking the throttle body openings did kill the engine.

thanks in advance
vince

 

I would venture to guess that you have a vacuum leak. Does that have the lines running under the upper intake? That's where I'd look. Did you plug the spout in when you pulled the codes?

 

the spout was plugged in during the code pull yes......

i'll have to look for those vacume lines but to be honest I have no idea where or how to find the leak.....

i tried propane straight down the air filter and it did now change the idle any at all....

I did disconnect the IAC valve and the slightly high idle is normal now...but reconnected it and continued to look else where as it is a new IAC.

next I pulled the rubber air intake tubes off and plugged the IAC holes with my fingers while it was still connected to the harness/truck and there was significant air being pulled through there....yet the truck still ran....is this pointing to a vac leak?

next I pulled the vac line off to the brake booster and plugged it....no change, with the IAC unplugged the truck still ran....

help help help please....

 

Yes, I believe what you did indicates a vacuum leak. If you follow the booster line, It should lead under the intake. There should also be other lines there. You can wiggle them or feel for any that are unplugged or pinch them off and see if anything changes. Also check the PCV hose for any cracks.

 

I cant find the pcv valve to save my life....

Still have a bad bad pinging at 3500 to 4000 rpms...part throttle pinging at 3000 rpms....

high idle continues to be a problem...

the brake booser line (plugging it that is) made no difference in idle speed.

I need some way to find broken vacume lines...

hey wait...I just checked my throttle stop screw...it seems as if someone (a ford tech) turned it inward some!! I unplugged the IAC and screwed the stop back until the paint marks from the factory matched...and bam! no more code 411...no more idle problem...yes!!

I have unplugged the computer to reset overnight and will see if the pinging continues!!! I'll get back to you soon...

vince

ps. keep the suggestions comming about the pinging though...there still might be a problem somewhere...

 

Only thing I can think of for a ping at those rpm's would be too much timing. You may want to recheck that now that you got the idle down. I was going to suggest looking at the plate but I thought you checked that. (musta got my threads crossed again) I can't believe a Ford tech did that.