A strange occurence.

[JT1]

I was sitting in my car while it was idling, today, and out of nowhere it starts freakin out almost stalling and then revving up repeatedly. Acted up for about thirty seconds and then stopped havent had a problem before or since.

Car is 88 merc topaz 140k.
In Closed loop when this happened(fully warmed up)
Car got mega rich when it was revving itself up to prevent stalling, i could see the black smoke from the tailpipe.

Whats going on. Bad IAC, TPS?

 

[94MaxGXE]

First thought, a little bad gas. Do you run a little STP fuel treatment or SeaFoam (both non-alcohol) at this time of year to address moisture in the fuel system?
Second thought, coolent temp sensor. Dirty contacts or bad sensor. ECU went back into open loop for a bit.

 

[lewdwig]

Or isopropyl alcohol. 94MaxGXE, do you find SeaFoam or STP fuel treatment to be better than isopropyl?

 

[tomcat27]

my first thought is a dirty IAC valve. (Idle Air Control) they get carbon on them. its an air bypass around the throttle plate that controls your idle speed. remove the wiring connector and the two screws holding it on. clean with carb cleaner - especially the cone shaped valve. also clean the backside of the throttle plate and the throttle body near the throttle plate. if you continue to have problems, find an OBD I scanner - the ford computers from that era are pretty smart. (motorola, I believe) and can frequently diagnose problems themselves.

 

[94MaxGXE]

Quote:
Or isopropyl alcohol. 94MaxGXE, do you find SeaFoam or STP fuel treatment to be better than isopropyl


Yes, about 110%. Why would you want to use alcohol when most of the fuel is blended 10% already? We all know ethanol alcohol in our fuel is nothing more than a government mandated clean air mandate.
We need to condition the fuel with synthetic additives that will remove moisture and provide lubricity such as SeaFoam, STP fuel treatment or even Lucas Fuel Treatment.

 

[ThirdeYe]

Originally Posted By: tomcat27
my first thought is a dirty IAC valve. (Idle Air Control) they get carbon on them. its an air bypass around the throttle plate that controls your idle speed. remove the wiring connector and the two screws holding it on. clean with carb cleaner - especially the cone shaped valve. also clean the backside of the throttle plate and the throttle body near the throttle plate. if you continue to have problems, find an OBD I scanner - the ford computers from that era are pretty smart. (motorola, I believe) and can frequently diagnose problems themselves.


That's what I was thinking. My car did this symptom once or twice before back when I first got it but it went away on its own, but I have heard that it's most likely due to the Idle Air Control Valve (IACV) as mentioned.

 

[eljefino]

TBI? I bet the injector started leaking. Coolant temp sender flakiness also a possibility. If there's a vacuum reference fuel pressure regulator it could have leaked fuel into the vacuum line.

Most other sensors would not have kicked up so much smoke. Also check vacuum line to MAP if you have it.

I think your IAC opening up was a reaction, not an action, and therefore not a problem. If it were goobered you'd have a funny idle but no smoke and it would have cleared out when you tapped the gas.

 

[mechtech2]

^^Great answer by eljefino!^^

 

[JT1]

Previous fill up i used b12 chemtool and it runs great with that stuff, i used MMO with this fill up-still runs good but not quite as good as with chemtool.

Eljefino, this car is MPFI, do you think if i had a bad CTS that it would show up on the dash gage or no?

I buy gas from the same station every time and as previously mentioned have not had any problems, could of got a bad batch though.

 

[demarpaint]

Originally Posted By: JT1
I was sitting in my car while it was idling, today, and out of nowhere it starts freakin out almost stalling and then revving up repeatedly. Acted up for about thirty seconds and then stopped haven't had a problem before or since.

Car is 88 merc topaz 140k.
In Closed loop when this happened(fully warmed up)
Car got mega rich when it was revving itself up to prevent stalling, i could see the black smoke from the tailpipe.

Whats going on. Bad IAC, TPS?



I'm scratching my head with a similar issue with an 88 E-150 4.9L. It has a surge upon hot restart, that is driving me nuts. I have checked and re-checked everything and have come to the conclusion as eljefino mentioned it is not an action but a reaction.

I'm thinking fuel injector problem since everything, and I mean everything is checking out OK. I had cold start issues, stalling, and after a high pressure FI cleaning and 3 treatments of RL FI cleaner I have resolved all of those issues and now started with the surge after a warm engine restart.

I'd suggest addressing the fuel injectors, if there are no codes and no vacuum leaks. Those older FI Fords had issues such as you mentioned.

 

[Warstud]

Sounds like a vacuum leak...with the hood up.. have someone shut off the car while you listen for a hissing sound to track down the leak.

 

[demarpaint]

In my case there are no vacuum leaks, something the OP might want to check as I had also mentioned.