Truck surges at startup when cold

[Wayne6197]

Hi. My 2000 Ranger revs up to around 2500 on cold mornings on startup. This lasts 10-15 minutes. Then it surges up to 2500, then back to 1500 or so every 3-4 seconds and will continue this until driven. I changed out the air control sensor, no vacuum leaks and thermostat is good per my mechanic. Any suggestions? Thank you.

 

[Uncle Gump]

It sure sounds like a vacuum leak...

What engine is it?

 

[Wayne6197]

Hi. It is the 3.0L flex fuel.

 

[Wayne6197]

It does not do it unless it is below 50-60 degrees or so.

 

[rubydist]

The other alternative is a sticky iac. If you cannot find a vacuum leak, I would change the iac.

 

[Uncle Gump]

Just an FYI...

I moved this to the 3.0L forum.

 

[bills4065]

It sounds like it is temperature related. You say your mechanic said your thermostat is fine.
Does your truck take a long time to warm up? A coolant temp sensor is a thermistor. One starting to fail can cause some some weird stuff.

 

[Wayne6197]

It sounds like it is temperature related. You say your mechanic said your thermostat is fine.
Does your truck take a long time to warm up? A coolant temp sensor is a thermistor. One starting to fail can cause some some weird stuff.

Thank you. I told him I thought it could be that but I guess he ignored me. Lol. Anyway I will change it and see. Thanks again.

 

[Wayne6197]

The other alternative is a sticky iac. If you cannot find a vacuum leak, I would change the iac.

I changed it but nothing. Thank you though.

 

[bills4065]

I am talking about the temp sensor itself, not the thermostat. I am not clear on your answer, does the truck seem to take a long time to warm up?

 

[Wayne6197]

Yes, I am talking about the coolant temp sensor. I noticed one of the wires was off of the connector harness so I ordered it and the sensor today. The truck seems to warm up ok, it just does that weird surging after a while then if I try to drive it before it stops that it is almost impossible to shift. I am hoping the temp sensor and connector solve this. If not then I'll try the MAF sensor. Thank you.

 

[gw33gp]

How old is the PCV valve? I had symptoms not exactly like yours but indicative of a vacuum leak. I changed the PCV valve, and the problem was solved.

 

[Wayne6197]

Probably the original one on the truck. So 24 years. Thank you. I'll check this out.