FoCo_4_Low

Hi Everyone! Glad to be back posting on this forum after a few years.

First off, the truck is a 95 4x4 XtraCab with 3.4 and 5 spd man.

Here is my issue, my truck idles strangely when it is cold. When I first start it the idle is anywhere from 1500-2000 RPM, which is too high even for having the cold-start fast idle (it didn't used to idle this high on startup). It will idle around 2K for 15-20 sec and then the ECU will kick something in and the idle goes to about 1250 RPM. Once I start driving and come to a stop light, the idle is sporadic, sometimes it drops immediately down to ~1000 RPM, sometimes it shoots up to 2K and stays there, sometimes it starts high and slowly gets brought back down. All of this is 100% dependent on the engine temp, the colder it is outside the worse it is but the kicker is all of this goes away once the truck warms up to normal operating temp. This seems to be a problem with the engine management system to me, one of the sensors hooked up to the ECU is going awry. Does anyone have any insight as to which sensor specifically could cause this, or where I should start checking?

Thanks in advance!

Terrys87

iTrader: (1)

Not saying this is your problem, but I did run into an issue on the dashpot on a friends truck a few days ago. It is like a physical stop by your throttle assembly. We just did a little adjusting on it and fixed his.

BamZipPow

Sounds like yer IAC valve is gunked up. Pull it off the bottom of the throttle body and clean all the carbon out of it. Make sure you don't dork up the gaskets or you'll be buying new ones from the dealership or the parts store.

FoCo_4_Low

Thanks BAM, was hoping you'd chime in with some insight. I'll definitely clean that guy up real good. If that doesn't do it, any other ideas? My next thought would be the MAF, I'll see what I can do to clean that guy up as long as I'm fiddling with the throttle body anyways.

BamZipPow

The MAF shouldn't make a that big of a difference when cold/warm. It would do it all the time as if it was dirty/damaged...the reading would be off spec all the time.

The only other thing that could be causing it would be the Engine Coolant Temp Sensor. You'll have to measure it with an multimeter along with the temperature yer measuring it at and report back. I believe it's located under the air plenum...not easy to git to.

Has yer vehicle been worked on before this happened?

FoCo_4_Low

Ok so here is the latest, I took off the IAC and the MAF this weekend and cleaned them both up with some carb cleaner. The IAC had some dirty buildup but was still working, the MAF was also dirty but working, I tested the resistances across the terminals on both of them and they are in spec (per my repair manual). This actually made the problem worse, It now roars up to about 2500 rpm when started. While driving, when I press the clutch in the engine drops down to about 800 and tries to idle there like it should for a second but then jumps up and down between 1000-3000 RPM repeatedly after going up and down 5 or 6 times it finally makes up its mind and idles steady around 1500 rpm. As before the problems get better when the engine is warm, they don't go away though. It still idles too high (~1200) and occasionally still jumps up and down before idling steady. Did I break something worse? I don't see how I could have made it worse with just a cleaning of some parts. Any Ideas? I'm way lost here?

FoCo_4_Low

To answer you question BAM, I do not believe the engine management system has been worked on before ever. All the parts I'm finding still have original Toyota stickers/markings on them, screws still have lock-tite on them, and everything is nice and evenly dirty. But that being said I am this trucks 3rd owner so I don't know for sure.

BamZipPow

Is yer check engine light on? If so, did you pull any codes?

Is the air intake hose cracked? How good are yer vacuum lines? Have you tried the starter spray method fer vacuum leak checks? It won't tell you where it is but it will tell you if you have one.

Did you measure the TPS (throttle position sensor)? Do you have any ODBII computer diagnostic setup? Auto Tap or Auto Enginuity are two that come to mind. An Ultragauge will do a little bit of information display but won't really git down the to the dirty stuff like the other 2 diagnostic setups.

Shoot some video of the problem and post it.

FoCo_4_Low

No Check Engine Light, which seems quite odd to me, but I know the CEL is working properly because I tripped it a few times connecting/disconnecting the sensors this weekend. The air intake hose is in good condition, I don't think I have a vacuum leak because that would trigger the CEL right? I'll definitely pick up a can of starter fluid and give that a try to double check. It stopped jumping up and down erratically and now just idles way to high. I need to check the TPS, it looked to be in good condition outwardly but I'll check the resistances on the terminals. Also I do not have an OBD II reader/computer, would be nice right about now though.

BamZipPow

Something that does come to mind...the shaft to the throttle body may be worn and allowing air in when the throttle plate is closed. Did you clean the throttle body before this started to happen?

There are a few threads (can't remember which site) that addresses this problem with a worn throttle body shaft. Some fixed it by replacing the throttle body...while other added in some shims. Try spraying around that area first with some starter fluid and see if the RPMs go up or not.

If you can find a shop (or can borrow one) that has a smoke machine and knows how to use it, you can find out where yer vacuum leaks are pretty quick. You'll need to be in a garage with no drafts though...

FoCo_4_Low

PROBLEM SOLVED!!!! It was the coolant temp. sensor. ECU though I was Florida instead of Colorado.

BamZipPow

Glad you figured it out. Did you remove the fuel crossover pipe to git to the ECT sensor? Since you had to tear down to the intake manifold...did you replace the valve cover gaskets while you were in there?

FoCo_4_Low

OK, so I was a little hasty with my last post, after a few days of driving THE PROBLEM PERSISTS!!! The ECT sensor did need to be replaced and the engine is running fabulously right now, except at idle. Still way too damn high when cold, a little too high when warm and "loping" up and down occasionally. I did have take off the fuel rail crossover to get a deep well socket onto the ECT, did't think to replace the valve cover gaskets though I should have! Any other ideas guys? After replacing the ECT my check engine light did come on, but my OBD2 port isn't working, i'll start another post on that though. If I can get the code hopefully I'll be able to get to the bottom of this.

BamZipPow

Did you measure the resistance of the old ECT sensor? Which end was it out of spec?

I would still check the TPS to make sure it's in spec. Don't just go replacing it to see if it fixes it.

As far as yer ODBII port goes, try replacing that 7.5A fuse in the kick panel fuse box.