Lowering fast idle at cold start

My fast idle rpm at first when started is like 1500. It will come down after warm up. What do you guys think should be about 1200 when first started I feel. What's the right way to lower the old start rpm but the rpm after warmed up is fine. 3.4 V6 '95 Tacoma with manual trans. Thanks

 

where does it idle after it has warmed up?

 

About 900

 

I could be wrong but I don't think you can lower it. It's ECU controlled by the IAC. If you think it's abnormally high try cleaning the IAC. But when my IAC fast idle is too low or doesn't fast idle when cold at all.

 

well, i've been chasing down a high idle for a while now, have yet to find the culprit, but I can tell you that, at least the FSM for my 1996 3.4L 4x4 5VZ-FE says that the idle should be 700 plus or minus 50. So anywhere between 650 and 750 is considered 'normal'.

Dont worry about your idle being higher when your cold start your truck, that is normal. Our 3.4s idle high until the engine is warmed up. from what I've found around here, depending on the temps outside between 1500 and 1200 is normal for cold start, but it should drop to about 700 once the engine reaches operating temps.

Im dealing with about 1750-2000 rpm at cold start, once its warmed up ill idle at 1300-1400 steady. Cleaned throttle body, idle went up to 2500-3000! Butterfly valve worn into the side of TB. Got a TB from junkyard in much better shape all cleaned and now im back to 1500 idle. Sound like your dealing with something slightly similar but less drastic. I was about to go out the door to Napa to get a new PCV valve and grommet and hose for PCV valve when I saw your post I thought id chime in real quick. ill let you know if the PCV valve is my problem.

Edit; grammar

 

Clean and check your IAC according to the FSM, make sure the port is clean also.

 

Back in my reckless twenties when I was driving Fords, I remember people on the Mustang and Crown Vic forums using a copper fitting with a hole drilled in it as an "IAC restrictor" to "fix" the factory high idle on their 4.6s. I tried it for a hot minute ; if you have Flowmasters it will totally make it sound like you have a wicked lopey cam setup. Fun, but pretty damn silly. I remember the stated logic being that if the engine revved lower at idle, it would save gas, when in fact the reason for the high idle when cold is to bring the engine to operating temp where it runs most efficiently as quickly as possible. Definitely feel free to clean your IAC and throttle body, but 1500 sounds normal to me.

 

You could sit down figure out what sort of signal is being sent to the ecm via the temp sensor to control The IAC

then design and build a circuit to produce the desired rpm your looking for .

I am not sure why you want to go through all that work and expense for a few rpm.

When the temperature drops below zero F my idle is up close to 2000 rpm then I seldom take notice anymore

 

1500 cold idle isn’t bad. If it’s real cold out mine idles about there and slowly drops. I’d recommend cleaning your IAC and see what that does. I accidentally washed some gunk in mine and had a 2000rpm idle when hot. Took off tb and IAC cleaned it and now it stays about 650-700 warm with no AC on.

 

I’ve got a fully warmed engine operating at 1500 this is twice what it should be. Should be 700

 

Have you replaced that tb yet?

 

Currently I have 2 TB's on hand. one is from a junked 3.4l engine, one is my original.
Original TB=TB1
Junkyard TB=TB2

TB1 has large gaps all around the butterfly and the butterfly has worn into the TB1. When I have this TB1 on my engine, my idle will fluctuate badly between 2000 and 3000, because the butterfly gets stuck on that groove that has been worn into the TB1..

TB2 is in much better condition, currently I have TB2 on my truck. With TB2 my idle is much steadier around 1400-1500(when warmed up at 165 degree engine temp) according to my Ultra-gauge

TB1 is most likely getting shipped out to Maxbore.com in the next few days, to get re bored and new butterfly machined.

Also, I have my EGR pipe blocked off at the exhaust manifold and the egr valve. 10k ohm resistor is in the egr plug to prevent CEL from coming on. This is not by choice, but have replaced that pipe twice and it has broken twice. When I put the resistor in place and cleared the code from the EGR pipe not being connected, my idle increased 250 rpms. (the complete opposite that I expected) I figured I was idling high BECAUSE of CEL, but removed CEL and idle increased slightly from 1250 to where I am currently idling. I dont think this is involved with my idling issue, but I could be wrong.

Another member had similar issues and the PCV valve was the culprit, my grommet is not rubbery anymore probably causing a vacuum leak.
I didn't make it to the store yesterday for a new PCV valve, so hopefully I will make it today, but now we've got snow and my shop is the uncovered driveway.....brrrr.

 

I've done this, and tested all electrical per the FSM. IAC valve motor operates both ways properly...

 

That is very strange, considering I guess it could be some sort of vacuum leak but seems you have covered your bases. Could be some sort of ecu issue? Where is this egr tube located? I don’t see any kind of egr on my engine anywhere. Did all 3.4 engines have egr?? Mine is a 99 prerunner

 

Mine has cold-started at 1600rpm since new. That's 17 years. Normal. What I always wondered though, is why the clutch fan runs so hard at cold startup when the engine doesn't require all that cooling.

 

Cold start 1600 is perfect, but Warm engine idling at 1600 is not normal. Everywhere in the it FSM says when the engine is warm the idle should be 700 plus or minus 50. I'm assuming your idle drops to around there when your truck has reached operating temperature?

 

When I left earlier my scan gauge said water temp was 69 and it cold idled on 1250. So if it was 40 or 30ish degrees I could see it hit 1500ish cold. But it should come down within several mins. Wife’s 4 banger idles at 1500 cold too.

 

Yeah it idles normal after warmup. I was specifically referring to cold idle.

 

Is it getting up to operating temp so the motor goes into closed loop? Use to be on most computer controlled engines it had to get to 190 to 195 or it will keep it rich because of the temps that it thinks it's seeing so it stays in open loop, rich condition. Just a idea to check.