insane high idle after In. Man. replacement

neathy said:

My intake manifold had a coolant leak so I replaced it (No parts left over !). But ever since I've had this insane high idle at start up that levels out to 2000 and won't go down. it's not throwing any codes but my rpm's go to maximum on crank up. I've taken off the IAC and plugged the hole with my thumb but nothing changes. I can't hear any vacuum leaks. It passed the bubble test. What do I check next ? 2003 mustang 4.6l manual, no previous problems. thanks in advanve,neathy

Click to expand...

Check your PCV valve and hose. My son had the same problem with his 95 Neon. If you just replaced your intake, I'm willing to bet one of your hoses when you did the reinstall is broken or badly cracked somewhere. Check each hose that you removed and replaced. You have to actually remove each hose one by one and check for cracks or if it is broken. I can almost garranty you will find one somewhere that is causing your rpm to raise up at start up. If all the hoses look good, replace your PCV valve. Good luck, Tommy.

no fix yet

No, I still have the same problem. No detectable vacuum leaks. The only way I can drive it is to unplug the MAF sensor and put it into limp mode. I've plugged the IAC valve, so I don't think thats the problem.I'll replace the sensor when I can afford it, but now I see OIL leaking from 2 fuel injectors ! I didn't even know that was possible ! One thing after another...never another ford. I've had 4 mustangs but this will be my last. I guess I'll drive it 'till it drops. Thanks, neathy

neathy said:

No, I still have the same problem. No detectable vacuum leaks. The only way I can drive it is to unplug the MAF sensor and put it into limp mode. I've plugged the IAC valve, so I don't think thats the problem.I'll replace the sensor when I can afford it, but now I see OIL leaking from 2 fuel injectors ! I didn't even know that was possible ! One thing after another...never another ford. I've had 4 mustangs but this will be my last. I guess I'll drive it 'till it drops. Thanks, neathy

Click to expand...

If you have oil leaking from your fuel injectors, that would support my original thought concerning your PCV valve. If your pcv valve is stuck in the open position, crankcase ventilation will end up inside your intake. Who knows, it then may possibly leak through your fuel injector 0 rings. You just never know. Try replacing your pcv valve. It's fairly cheap, nothing to lose. Good luck, Tommy.

Just a thought. I'm not a mechanic, have you checked to make sure the butterfly valve on the throttle body isn't stuck partially open?
I had this happen to me in traffic once. Pulled up to a red light in neutral and I was idling at around 3000 rpm. Freaked me out. I was able to drive to a point I could pull over. I had recently installed a 75mm TB and immediately thought of that. Turned the car off manual opened and closed the valve in the engine bay, checked to make sure the throttle cable wasn't binding. Turned the car back on and it was back to idling correctly. It's been about 3 months and hasn't happened since.

One more thing about the fuel injector oil leak. Which injectors does it look like are leaking? I thought I had a leak at my two front passenger side injectors because oil was pooling around them and my two front plugs. It was actually coming from around my oil filler neck which is sealed with a bead of silicone, rebeaded the neck, problem solved.