Stalling out

[Nathan123]

I have a 89 bronco II. When your driving, and step on the brake and stop, like at a stop sign, sometimes the rpm surges say down to 500 and then up to 1500. Sometimes it stalls out but if you give it gas quick enough it will recover. Normal Driving is not affected. I cleaned the IAC valve and it did not help. I asked my mechanic and he recommended a ford fix part...its a plate with 3 adjustment screws that goes between the IAC and intake. Turns out mine already has this. Adjustment of the screws helped for some time but about once a month this surging would start back up. So I finally replaced the IAC valve with a new one from autozone, and the problem continues. I havnt pulled codes yet, but previosly the only code thrown out was "cannot control idle during low RPM self check" I think its number 13. Any ideas?

 

[WTF]

Check to make sure your timing is set properly. Other than that, it sounds like your transmission isn't getting the info that you are coasting or stopping so it's not unlocking your torque converter which will stall or kill the engine.

 

[kimcrwbr1]

When was your last tune up plugs, wires ,cap,rotor, PCV. It is time to winterize if you dont know how old the wires and PCV are change them your symptoms could be alot of things start with the basics first then go from there. Good tune up, filters and oil.

 

[adsm08]

I doubt it's the converter staying in lockup. That usually acts more like a stick when you don't put in the clutch.

I'm with kim, do a total tune up, filters, fluids, plugs, wires, cap, rotor, and an O2 sensor. I had a bad sensor do that to me once, and they are supposed to be changed every 75 to 100K miles anyway.

 

[WTF]

I doubt it's a tune-up fix otherwise he'd posted about his truck running like crap all the time not just when coasting or stopping. Make sense?

 

[Nathan123]

Yea it always has good oil, it had a fuel filter and PCV valve last year, new plugs last winter (autolite) and the plug wires that came with it look pretty new so I've been trusting them (still really dark blue, nice writing, soft and flexible). Bought a timing light for 60 bucks when I did the plugs so I could check it just cuz, and it was perfectly on the mark. What tells the trans that the brake is on or your coasting? I also just realized I can take that plate with the adjuster screws out and mount the IAC valve like it came from the factory and see if it works right.

 

[Shran]

I could see a vacuum leak possibly causing this - as the IAC attempts to compensate for the leak when the engine is at idle. Something to think about anyway. I doubt this is tuneup related too.

 

[WTF]

Any updates on this?? You can find vacuum leaks easily with a propane bottle that's turned-on but not lit and pass it by each vacuum line connection and any other intake related connection while the engine is running. The engine idle will rise a tad if there's a leak. You can also "reset" your kickdown cable. It may be too far and be tricking your transmission with the incorrect throttle position. Hope this helps.

 

[Nathan123]

I'm at school right now but this weekend I'll have a look at it when I get home. How do you "reset" the kickdown cable. From the pedal end or the trans end? I'm not quite sure what that would involve. Has anyone heard of the aluminum plate with the two adjusting screws on it that goes between the IAC and Intake? I plan on taking that out and mounting the IAC right to the manifold like it was from the factory for starters. I have a suspicion that the miscellaneous vacuum lines have some leaks though. I'll post what I find out, and if I hit a brick wall.

 

[Shran]

I have never heard of that plate thing, doesn't mean it doesn't exist though. Can't hurt to try without it, just make sure you use new gaskets.

For vacuum leaks - I would check the lower intake and plenum gaskets first, before anything else. I have seen multiple instances where these were literally crumbled into pieces that had to be vacuumed out.

 

[Nathan123]

Heres the plate thing I'm talkin about. The front of it is shaped like a trapazoid, and the screwes are on each of the three flat surfaces (you can only see one in the pic) The screws have an allen head. This was a ford part, my mechanic gave me one to fix the problem I described, he had it on the shelf from years back (he said it was that common) and wanted to get rid of it. I gave it back to him because I have one already and didn't even know it. I've never heard or read anything about it on hear. I hope it isn't the intake gasket

 

[Nathan123]

Well that picture didnt go the way I wanted it to I'll try again. You can actually make out 2 of the adjusters.

 

[Psychopete]

Look for carbon build up on your throttle body plate. My 2.9L was never real bad, but it never seen a decade of use w/o being cleaned. Took a TB off a Tempo engine that I don't think had ever been taken off, carbon build up like crazy, which is going to affect what air flow should be at idle past the plate (it's pretty much "clogged"). Symptom of a carboned TB is dropping RPM or stalling when stopping. Just something to check out, cause it will affect IAC function - which seems like you're trying to band-aid something that's not the problem. You shouldn't need that IAC plate.

 

[Nathan123]

Thanks for that suggestion that sounds a lot easier than changin the intake gasket. I know when I cleaned the IAC it was really crusty so the TB being dirty sounds logical.

 

[WTF]

As posted in the Autozone Tech pages:

"The kickdown cable is self-adjusting over a tolerance range of 1 in. (4mm). If the cable requires readjustment, reset the by depressing the semi-circular metal tab on the self-adjuster mechanism and pulling the cable forward (toward the front of the vehicle) to the "Zero'' position setting. The cable will then automatically readjust to the proper length when kicked down."

Hope this helps!