TBI surging when idling after warm. Coolant Temp Sensor replaced. Cause?

[89Fleetside]

1995 Fleetside 5.0L AT. Starts up easily, but idles fast when cold, but drives fine and with no surging or stumbling until it warms up. Once warm, it will die at stop signs/light, stumble badly when accelerating, and surge from a rough low idle to a fast idle at times. Changed the Coolant Temp Sensor as that seemed to be the most discussed problem part for these kinds of issues and it was a simple and cheap part to replace, but had no effect. I know it may be the fuel pump, the TPS, or the ICM, or other things. Rotor and cap inspected and appear fairly new, no cracks or visible wear, clean and serviceable. What would you check first?

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[AuroraGirl]

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Codes...?

 

[89Fleetside]

Codes...?

None that I know of.

 

[AuroraGirl]

None that I know of.

So you never checked. Of course you wouldnt know. Check

 

[89Fleetside]

Don't really need the attitude, and I don't have a scan tool for this truck. So thanks anyway. I am sure someone has experienced a similar situation and will have some knowledge and insight on where to begin.

 

[AuroraGirl]

Don't really need the attitude, and I don't have a scan tool for this truck. So thanks anyway. I am sure someone has experienced a similar situation and will have some knowledge and insight on where to begin.

What year is your truck? If its a 94 and older its probably easily checked with a paper clip. if its a 94(maybe) , 95, it may be slightly more difficult, and a 1996+ isnt TBI if I am correct in believing that, so the attitude was because I thought you were being lazy. You seem to just not know about this , which is not lazy ness so I do apologize.

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[Schurkey]

I don't have a scan tool for this truck.

Verify fuel pressure.

Inspect/replace all the usual "tune-up" items--cap, rotor, plug wires, plugs, PCV system, EGR system, initial timing, AIR system, etc.

GET a scan tool, verify EVERY sensor and computer output.

 

[thinger2]

Always start a question with year, model, engine, transmission.
These things changed so much over the years that we really need to know that.
Based on your user name Im going to assume that this is an 89.
Theorectically 95 and older are all OBD1 systems.
OBD11 is 96 and newer.
But, 95 vehicles are so odd that they are pretty much a "stand alone" one year only variation.
You can check for codes using the paper clip trick on an OBD1.
Really easy to do.
As long as you have not disconnected the battery or let it sit untill the battery went dead.
If you disconnect the battery on a ODD1 system all of the parameters that the ecm uses to control the engine are lost.
And so are the codes.
When you restart it again it needs to "relearn" from those inputs before it will run properly.
If this is an 89, it has two temp sensors.
One in the passenger side cylinder head.
That one feeds signal to the dash temp gauge
The other one is on the pass forward side of the intake manifold.
That feeds the ecm.
Whenever you crack a sealed system open you have to purge the air out of it.
If you pulled the head sensor and let it drain I gaurentee that you air in the cooling system.
If you pulled the manifold sensor and it was not full right to the top?
You have air in the system.
At hot idle I would be kinda surprised if it caused the ecm to firehose fuel like it is but it could be some ecm base module to keep it from being to lean.
Even over my crappy celll phone it looks like a major injector pulse issue.

Why did you replace the temp sensor?
What was going on before that?
Were you having problems before you replaced it or was everything fine untill after you replaced it?
Give us the back story with as much detail as you can.
I think you have maybe an air problem but you need to check fuel pressure for sure and set your timing with the dist wire disconnected.
Start with the basics.

 

[tayto]

yes start with basics. also vac leaks can cause surging. check/replace throttle body gasket, cleaning IAC+ doing minimum air adjustment. also check play in the throttle shaft, this is one that gets overlooked and is a common wear and vac leak spot.

 

[PlayingWithTBI]

If you disconnect the battery on a ODD1 system all of the parameters that the ecm uses to control the engine are lost.
And so are the codes.
When you restart it again it needs to "relearn" from those inputs before it will run properly.

The code(s) will reset. The only other thing the ECM resets is the INT (Integral AKA short term fuel trims) and BLM (Block Learn Multiplier AKA long term fuel trims). It'll run on the VE tables in Open Loop until it goes into Closed Loop, then it'll start working on INT and BLM based on O2 sensor feedback.

If this is an 89, it has two temp sensors.
One in the passenger side cylinder head.

Driver's side for the gauge. Some later models with E-fans used a temp sensor in the passenger side for controls.