'94 Ranger 3.0 constant high 2k idle

[christw]

Hey guys... looking for some diagnostic help. '94 3.0 5sp 2wd with 212k miles.

My truck's idle has been working it's way up progressively as I've been doing work on the truck. I recently got it back from a clutch/oil pan/rear main replacement after it was dumping oil everywhere. They also fixed a leak at the right side exhaust flange. It came back with the 2k idle that was previously 1600-ish. On starts it'll get as high as 2600 and work down to 2k. It bucks like hell if I clutch it down to anything under 1500. It's also been surging a bit between 1700 and 2k randomly.

Thus far I tried unhooking the MAF and temp sensor and got codes, no change. It will idle at 1100 occasionally on random cold (0-40 degrees F) starts. If I reset the electrical system it starts at 1700, drops idle to 1100ish and works its way back up within about 20-30 seconds. This is warm or cold.

New parts on the truck (probably all irrelevant):
r/s cylinder head
IAC
clutch
oil pan gasket
rear main seal
upper/lower rad hoses
r/s exhaust flange repaired for a leak

I just remembered that I was told that there was a problem (leak) with the a line off of the exhaust by a mechanic who did the head replacement. I think it might have been for the EGR? Could it be that simple?

 

[black_demon69]

check for vacuum leak. vacuum lines, intake, brake booster for starters. also verify tps sensor is working within parameters

 

[Road Angels]

break out the diagram for the vacuum system make sure every thing is routed correctly, an while going over it look for cracked hoses, cracks in plastic spliters, as well as every thing mentioned by demon69, also check to see if egr is stuck open or is opening when it should not be like at idle, pull the line and plug to see if that helps, being its had a lot of work some thing may have been left loose or not connect right

 

[97ranger xlt]

a bad pcv valve will cause a high idle and not throw a code....

 

[christw]

I checked and swapped the PCV valve, it's fine. Brake booster line is brand new, intake gaskets were last done with the head replacement (1k miles ago) but the oil pan, clutch, rear main, and right side exhaust flange repair were done since then. Again, I seem to recall the mechanic who did the head warning me that I had an issue with the EGR tube. I'll investigate that and test the TPS later today. I'm not fond of chasing vacuum leaks on a noisy engine in the snow so I'll go for the easier stuff first.

 

[RonD]

Warm up engine, shut it off
Disconnect IAC valve
Restart engine
It should idle at about 500-600rpms so barely running

If it is higher then there is "unreported" air coming in without going thru the MAF, this can be a regular vacuum leak(engine side of throttle plate) or a ported vacuum leak(MAF side of throttle plate)

With IAC disconnected and engine idling, remove one vacuum line at a time and plug the intake hole with your finger, if idle drops to 600 then you found the leaking system.

Also often over looked is the mechanics of the throttle plate, maybe throttle cable or cruise control cable(if so equipped) is holding throttle open a bit.
Shut off engine remove cables and restart, see if idle drops

 

[christw]

Warm up engine, shut it off
Disconnect IAC valve
Restart engine
It should idle at about 500-600rpms so barely running

This is the case. I bought the truck with a bad IAC and it's been idling high ever since.

If it is higher then there is "unreported" air coming in without going thru the MAF, this can be a regular vacuum leak(engine side of throttle plate) or a ported vacuum leak(MAF side of throttle plate)

With IAC disconnected and engine idling, remove one vacuum line at a time and plug the intake hole with your finger, if idle drops to 600 then you found the leaking system.

I'll get on that soon. I just found a canister with a sensor on it labeled CANP on a vac line diagram unhooked by the battery. It's a start. Would my tank's filler neck being cracked also contribute to the vacuum issue once I hook this line back up?

Also often over looked is the mechanics of the throttle plate, maybe throttle cable or cruise control cable(if so equipped) is holding throttle open a bit.
Shut off engine remove cables and restart, see if idle drops

No cruise sadly. I used a zip tie spacer on the throttle cable to remove pedal play. I'll check the plate and cable again in just a minute.

 

[swynx]

Try unplugging the 02 sensors

 

[christw]

I reattached the little bugger to the carbon canister and it's idling at 1100 again! Woo! I need to replace and further diagnose some of the lines but it'll do for now. The throttle assembly is fine.

Confusingly, even though I've mentioned it 40 billion times, my truck has no EGR. Facepalm moment right here. I think my brother is actually the one who brought up EGR with this truck... oops.

 

[RonD]

"Cable mod" can cause high idle if you take out too much slack

CANP is part of the EVAP system, EVAP pulls gas fumes from tank while engine is running, it does use the vacuum system and the EVAP system is based on the fuel tank being air tight, so yes a leaky filler tube or vent tube effects the EVAP
CANP = Canister purge valve

 

[christw]

I did the throttle cable when I had a bad IAC and noticed no difference at the time. It has play in the cable but I'll still check it out. I'll also test my TPS soon.

I need to replace several runs of vacuum tubing and invest in some clamps at the least. If I disconnect the EVAP system will bad things happen? It had popped off at the front side of the canister purge valve. I didn't get a CEL for the two days I drove it like that.

 

[RonD]

No, nothing bad will happen, you should get a CEL eventually

 

[christw]

Good news! I gave in and did the MAF-HUGE improvement under 2k, especially when it's cold. I also sealed off the leaky EVAP. My idle is consistently ~900 until the engine warms, including mid drive stops. Then it's back to 1500 when it's warm. Drops to 1kish if I restart the truck warm until I touch the throttle.

I think (key word) I've got it sorted out besides the O2 sensors.