cant hold an idle while once warmed up

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Nov 17, 2005 | 10:32 PM

tsiawd1028

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cant hold an idle while once warmed up

hey guys i have an 87. I just tested the fuel pressure today, and its fine. WHen my car is cold , it will start right away, run smooth, and not surge.

But once my coolant temp reaches 125 degreed F. , the idle starts to get rougher, and by 140 F. the car is missing badly and wont hold idle on its own, it will stall.

Also the previous owner has installed an air/fuel gauge which is connected to the stock o2 sensor. I know the the o2 sensor wont start cylcling, until it is warm, But with the coolant temp around 150, car idleing for about 2-3 minutes, the o2 volatage isnt cycling yet. Could this be pointing to a bad o2 sensor? or is it usally to take longer for the o2 sensor to operate?

Nov 18, 2005 | 01:08 AM

tsiawd1028

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n e 1?

Nov 18, 2005 | 01:16 AM

cv67

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From: altered state

St. Jude Donor '05

Pulled any codes? Mine does the same thing, got a code 43-EST(electronic spark control)

Nov 18, 2005 | 02:24 AM

Mo_Bandy

Melting Slicks

Joined: Dec 2000

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From: Fremont Oh

You might check your IAC Idle air control it may be carboned up, so as the car is warning up it cant compensate ...

Just a thought ....

Mo

Nov 18, 2005 | 07:09 AM

Ivory90

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From: Beach Cities SoCal

Obtain the any queued up code is the key...I had a similar problem I was throwing a 44, today I replaced the O2 sensor, problem thwarted for the moment.

Nov 18, 2005 | 08:15 AM

bogus

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From: San Pedro CA

I am thinking that it is definately ECU related... allow me to explain!

At those temps, the ECU starts to read sensors, and not depend on internal tables, hence, the data it is getting is bad...

I would check codes and see what is going on. Also, some sensors will be weak or slow and give poor performance without throwing a code.

I would be diagnosing the EGR, MAS and O2.... at the very least.

Also, check all the wiring... pre 1991 Corvettes (well, all GM cars, actually, and more than likely all domestics) had a different insulation wire composition. The older stuff has a tendency, over time, to become brittle, shrink, crack and rub away. This leads to shorts and other problems. I would check the harnesses that rest on the intake base... make sure there are no chaffed wires in there.

Last edited by bogus; Nov 18, 2005 at 08:19 AM.

Nov 18, 2005 | 11:50 AM

CFI-EFI

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From: The Top of Utah

I would be concerned with what that wiring from the O2 to the gauge to has done to the signal being received by the ECM. I would start by seeing how it runs with the O2 disconnected from the gauge.

RACE ON!!!

Nov 18, 2005 | 03:43 PM

tsiawd1028

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thanks for the great answers, im going to go check out how they wired the airfuel gauge, im pretty sure they just spliced it into the o2 sensor harness, hopefully not on the ecu side.

I totally agree with you bogus, It does seem that once the car is starting to go into closed loop, the car starts screwing up. Any easy checkes for the mass, and egr?, I know how to check the o2 sensor.

The only code i got is for low fuel pump voltage. The previous owner had hotwired the pump. And i dont know why? Even if the relay was bad, the oil pressure switch would start the fuel pump as a backup?

I assume the low fuel pump voltage, wouldnt cause the problem of the stumbling only when the car is warm, it would mess it up all the time.