Unusual Idle Problem
07-13-2017, 10:58 PM
#1
3rd Gear Member
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Join Date: Jul 2017
Location: AZ
Posts: 849
Unusual Idle Problem
Touched on elsewhere, not thread specific, so asking for info. '94 GT, 5 spd., 161K, runs real well, for the most part. Start, drive, eng. gets to operating temp., no problems at all. Shut down, restart in say 10 minutes, eng. starts normally, rpm up to ~ 1100 just momentarily, then drops too low, ~ 500, jumps up again, drops again, jumps up again, then drops below 500 and eng. dies. If I start, hold throttle open ~ 1200 for several seconds, let off, eng. idles normally, ~ 700 - 800, AC full on. No load, (AC), same effect.
Have brand new 5.0HO in the corner, so yanked it's entire Throttle Body off, TPS & IAC intact, installed on car, same effect. Past work in last month, not really relevant, new plugs and cap & rotor.
I'm wondering about Engine Coolant Temperature Sensor, bad would throw a code, or not? Probably not, IMO. O2 Sensors? Would appreciate thoughts. imp
Have brand new 5.0HO in the corner, so yanked it's entire Throttle Body off, TPS & IAC intact, installed on car, same effect. Past work in last month, not really relevant, new plugs and cap & rotor.
I'm wondering about Engine Coolant Temperature Sensor, bad would throw a code, or not? Probably not, IMO. O2 Sensors? Would appreciate thoughts. imp
07-15-2017, 12:35 AM
#3
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Thread Starter
Join Date: Jul 2017
Location: AZ
Posts: 849
Have not done that, but like the suggestion. Didn't because Throttle Body containing Throttle Position Sensor & IAC, all brand new, were thrown on engine, problem the same. Today, I think I solved it. BTW, no CEL, (MIL), others tell me codes might be set without CEL. Don't know about that, wish I did. WTF good are codes set if you don't know they are there. Think the guy's full of ****.
So I wondered, OK cold, NFG hot, what might be sending bad info to PCM? ECT, Engine Coolant Temperature Sensor. Changed it out today, drove to store, engine got hot, ran perfect both cold and hot, shut off, went in store for.....mmmmm St. Pauli Girl GERMAN BEER, $11.99 per 12!
Car started like an explosion, BOOM, like good 5.0s start, right away settled down on idle point, 750-800 rpm, rock steady. Turned on AC full blast, tach didn't even quiver. Think I got it! imp
07-21-2017, 02:02 PM
#4
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Join Date: Nov 2013
Location: RI
Posts: 254
It sounds like you may be experiencing an issue with "after start enrichment". This would be masked during the initial cold start, due to the engine being cold and already running a "warmup enrichment"