Car shut off in Park, common culprits?

[GMUE03]

Hey guys. So today I was driving my 89’ Grand Marquis and as I pulled into a parking spot and put the car in P it immediately shut off. I restarted it and it idled a little funny for a couple seconds then seemed to run normally. Normally I would suspect the IAC valve, but wouldn’t that make my car turn off in Drive too? What do you guys think?

I plan on putting a smoke machine on it tomorrow to look for vacuum leaks.

[GMUE03]

To clarify, by “shut off” I mean it stalled, don’t want to confuse this with a no power/battery issue.

[GMUE03]

Update: drove the car around some more, it stalls out every time you take it out of a drive gear it seems. Went from Drive to neutral and it died. Starts up and drives fine though. Very interesting.

[friskyfrankie]

You will need to do a complete diagnosis but it sounds like an IAC issue.

[GMUE03]

You will need to do a complete diagnosis but it sounds like an IAC issue.

Agreed. I’ll note any vacuum leaks and clean the IAC just as a precaution. I do hear a hissing from what I assume is the automatic parking brake release, I wonder if a vacuum leak like that could cause drivability issues…

[friskyfrankie]

An accumulation of vac leaks (unless it is a big one) may cause driving issues and I would certainly seek out and repair them no matter how small. However, the stalling is probably a big one or IAC. I usually replace them (with an OEM if it can be found) and clean the ports real well also.

[tbear853]

Not a box, but a '98 or '00 CVPI work car, once was not idling. Was on a week of midnight shifts, didn't want to make a day trip to the dealer. A short, "easy to trim to adjust" piece of vacuum tube over the screw adjuster thread end worked until I got a new IAC from the dealer.

[sly]

Check the wiring to the IAC and if you have an analog volt meter, the TPS. A digital one won't help much because you want to see if the TPS has any dead spots (typically near the resting position when they do go bad). The needle on the meter will twitch at some specific spot if the TPS is bad instead of a nice smooth sweep as you open the throttle (engine OFF of course).

[GMUE03]

Update: I put my smoke machine on the car and really couldn’t find any vacuum leaks. I plumed the smoke hose into the butterfly valve on the upper plenum. I also took the IAC valve off and cleaned it (didn’t look extremely dirty) with no difference.

[GMUE03]

I plan on getting a Ford OBDI code reader today. Maybe I’ll uncover some stored codes

[GMUE03]

Update: took the car around the block and it drove fine. No weird misfires or anything. Upon putting the car in park it sputtered out and died. Once it restarted it it had a very strange idle surge. Giving the car some throttle input seemed to fix it. I took a video of this. Link: https://youtube.com/shorts/0dbJJZOpn...qT4A90DJLegBat
(Exhaust is getting fixed)

Maybe this symptom will ring a bell to the 5.0 EFI guys out there…

[sly]

Could be the TPS. If it has a dead spot right near closed throttle position, that could be causing this. If it's thinking the throttle is wide open when it's not, it'll close the IAC.

[GMUE03]

Could be the TPS. If it has a dead spot right near closed throttle position, that could be causing this. If it's thinking the throttle is wide open when it's not, it'll close the IAC.

After digging on other 5.0 EFI vehicle forums I also thought of this. I got my ODB1 code reader today and will use it tomorrow, hopefully this will point me in the right direction. I’ll keep this updated!

[GMUE03]

Ok, I put my OBD1 code reader on the car today and with KOEO I only got one code which was 34. I read online that 34 is EGR related. Maybe this is my culprit?

[sly]

Could be the EGR, but unless you know the TPS is good, it could be opening the egr because it thinks the TPS is in a cruise position. TPS controls a lot of stuff, so it's always good to make sure it's not bad first.