Stalling while cold engine, improvement when warmed up

[rsolis]

Hey guys. Need some GMN brainpower on this one.

87 Grand Marquis
139K miles

On a cold engine if I start the car it will run for one second than stall out. Only way to keep it running is to give it some gas. Once the car has fully warmed up stalling won’t happen on idle but it still idles rough. Now this happened in about a week and progressively got worse as the week went on.

When I drive it you can tell something ain’t right because there isn’t a lot of power and the car tends surge a lot while driving. Again. Way worse the colder the engine but it’s always there.

Got two codes:

Codes are saying

R41: O2 Sensor Voltage low/system lean

R91: O2 sensor Signal out of range/always lean

O2 Sensors are original. My question is will bad sensors cause the symptoms I’m getting? Or should I look elsewhere as to the the problem.

The TPS is within voltage and the IAC motor is functioning and sealed. Engine timing is also correct. We had to replace the ECM a few months back because it died so I don’t think it’s that either.

Thoughts?

[gadget73]

The oxygen sensors do nothing until the engine is warmed up so that won't be your cold start issue. Both sides showing lean tells me possibly a vacuum leak, clogged fuel filter, or maybe clogged injectors. Not impossible the sensors are bad but they don't tend to code when that happens, and both going at once is not so likely.

Check the air and coolant temperature sensors. They will have a lot to do with startup and fuel mix.

[rsolis]

Is if it helps the surging is very rhythmic like someone breathing.


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[Toploader]

I had the same symptoms on my '86, replaced a ton of shit.....nothing helped........now I get rough idle when cold, and surge, when hot goes away.....I am done tossing cash at this.......even if it is a Tudor

Is if it helps the surging is very rhythmic like someone breathing.


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[rsolis]

I had the same symptoms on my '86, replaced a ton of shit.....nothing helped........now I get rough idle when cold, and surge, when hot goes away.....I am done tossing cash at this.......even if it is a Tudor

Ugh

If you figure it out lemme know lol. I’ll do the same. It’s annoying.


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[Toploader]

Will do!!

Ugh

If you figure it out lemme know lol. I’ll do the same. It’s annoying.


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[knucklehead0202]

Definitely do the IAT and ECT sensors. My first '90 did the same shit until both of those had been replaced. Also check for vacuum leaks, i had some of those too...

[gadget73]

yes, vacuum leaks.

Check the timing too. Both will make these run stupid if not right and tight.

[rsolis]

Can anyone do a quick walkthrough on how to test and the numbers on the multimeter I should be looking for? for the two sensors?

I’m gonna triple check for vacuum leaks again today.


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[sly]

ECT: http://www.grandmarq.net/oldfuelinjection/page28.html
ACT/IAT: http://www.grandmarq.net/oldfuelinjection/page29.html

[rsolis]

Compression test all cylinders at 130PSI. Changed the spark plugs while I was at it below are pics. Gonna test those sensors tomorrow didn’t have enough time.




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[sly]

Looks like half are flat worn out and the other half are getting there. Time to replace plugs.

[DerekTheGreat]

Yeah, those were overdue. Looks to be burning the ole midnight oil too.

[rsolis]

Are the Ambient Air Temp and Intake air temp sensors the same thing? I’m seeing both terms used online and in all data. And one more thing and I thank you guys sooooo much for everything: where is the Intake Air Sensor located. I know the Coolant Temp Sensor is up front where the water hose is connected

[VicCrownVic]

No, Ambient Air Temp sensor is for cars with ATC. My AAT is plastic, and my IAT is not. If you have manual heat/ac controls then your car may not even have the AAT.
The Intake Air Temp sensor is located on the driver side of the lower intake, forward of center of the intake iirc.

Edit: IAT is also often referred to as the Air Charge Temp sensor or ACT.
As seen in the pic below labeled ACT:


The coolant sensor on the left in that picture (pass side front) is the important one that you would care about. The coolant sensor on the right in that picture (driver side front of lower intake) is only for the idiot light on the dash.