98 S-10 4cyl

My 98 s-10 cuts out while driving and the idle speed constantly changes when the temp falls below 32 degrees. The problem is bad enough that it caused the U-joint at the rear axle to fail. When the average temp is above 32 it runs fine.

Lest’s see. The idle speed is changing as you drive? How can you be driving with the engine is at idle?

Automatic transmission? When was the fluid last checked, changed w/filter change?

How did you determine that the rear axel failed because of this problem?

How about other maintenance items like the plugs, wires, air and fuel filters???

I seriously doubt this idle problem caused your u-joint to fail. U-joints on these trucks fail rather frequently when they get to this age. I have replaced dozens of them. If you have a check engine light on, you could start by pulling the codes and letting us know what you have, preferably by number, not definition. If no codes, the best way to figure it out would be for the truck to spend some time with a quality scan tool (MT2500, Determinator, Tech 2, etc. Not a code reader) to monitor engine and emissions control sensors to determine what is out of range and causing this issue. Since the problem seems to be temperature related, I would suspect either the engine coolant temp sensor or the intake air temp sensor.

Check for water in your air filter housing.

I do a lot of stop and go driving and in 1st gear with my foot off the clutch and idling it speeds up and then drops back to normal idle speed. Fluids and filters are up to date, plugs are only a couple of years old and I tested the continuity of the plug wires and they seem fine.

When I’m driving at normal speed the power drops off completely and then returns just as quick causing a whiplash affect on the driveline. I have a basic code reader and I get no indication that the computer is picking up on the issue. I will check the intake temp sensor (wasn’t aware of that) because it seems closely tied to the outside air temp. TYVM

Dry as a bone.

If I unplug the IAT how should it react?