cleaning tb/iac

ttocs · Oct 12, 2011

I have been having problems with my idle from time to time and wanted to start simple and clean the TB/IAC. My problem is that the studs comming off of my intake are a little off and I am afraid I will mess up the threads if I take the tb off of the intake. Can I just leave it on the intake and clean it there, leave it to dry completely for a day or two before starting it?

CC'S95GT · Oct 13, 2011

you can leave it bolted up.just spray TB cleaner in it and let it sit for 30 minutes. it evaporates fast.You may as well clean the MAF too while your there.I was having hanging idle issues. I replaced the stock TB with a (65mm), TPS and IAC all at the same time. and all that cured my problem. afterward I put an ohm meter on the old TPS and slowly cycled it through it's full range and I found a dead/flat spot with the meter.

ttocs · Oct 13, 2011

its an intermitten problem, some days it fires up from cold perfectly and idles great. every third or forth start it will fire up, rev to 1500 rpms, I hear a click(like a relay or a selenoid) and then it drops to 500-600 before dying.

ttocs · Oct 14, 2011

replaced the dist cap this morning as well as cleaned out the tb and it fired right up and seemed much smoother, idled lowe/better. It was the stock dist cap with 111k on the clock and looked pretty cruddy inside. Ups should be dropping off the coil shortly and that will be on next.

CC'S95GT · Oct 14, 2011

did you go with a msd cap or a a stock replacement?
I actually noticed an increase with the MSD cap and rotor.

ttocs · Oct 14, 2011

went msd on the coil(stock replacement) and the dist cap and rotor, and I spoke too soon. Got the coil today and put it on this evening. Started it up and it did the old trick where it revved up a little, clicked, dropped down to 4-500 rpms before dying out. Car ran like crap the entire night, died at two lights and was jerking under light acceleration.

What should I look at next?

toyman · Oct 15, 2011

Have you cleaned the MAF sensor element and checked the TPS voltage?

ttocs · Oct 15, 2011

I have not cleaned the maf because I just upgraded to a lighting maf less then a month ago and got a new one. TPS will be checked this morning.

CC'S95GT · Oct 15, 2011

I'm leaning toward the TPS. especially if it's the origional.
The TPS is a rheostat just like the dimmer on the wall for your house lights
You have a specific voltage going in and as you move the throttle body butterfly, the voltage increases and tells the computer how much fuel to add.
Over time the TPS will get a dead spot where the TPS spends most of it's time. So it sends the wrong signal to the computer and you get the rpm spike or a hanging idle.
It's easiest to test with an analog meter but it is possible to ck it with a digital meter if you go slow enough and watch the ohm reading carefully.

ttocs · Oct 15, 2011

ah that would make sense then, I have a degree in electronics and have dealt with dirty pots/rheostats many times.... There seems to be a temp componant to it so the expansion from heat might be putting it in the sweet spot where the cold area is still dirty. I think I will just save myself the time of diagnosing it and put a new one on it as(probably do the IAC as well) and just check it/set it once. This car was originally my mothers and I have no intention of selling it so I am just replacing all the old stock componants as they come up now.

CC'S95GT · Oct 15, 2011

degree in electronics? Nice. Obviously I'm explaining that to the wrong person. lol
I hope someone else will get some knowledge out of it.
sometimes it's easier to beat you head on the wall than to chase electronic gremlins

ttocs · Oct 15, 2011

went out and checked it and found 3 spots where it was acting like a dead short, no wonder it would die at random times.... Went to 4 different stores today to find the TPS and the IAC. Found the iac the tps is commin in tomorrow.

toyman · Oct 16, 2011

As you probably know electronic sensors such as the IAT, O2's and the ECT with age just don't respond as well as when they were new. These 3 sensors are also critical to proper engine performance.

ifinditunderground · Oct 16, 2011

Ok, now I have a question, how does one test the voltage on the TPS? I'd like to check mine now, but don't know where to start.

ttocs · Oct 16, 2011

I had to check my haynes manual, section 6-11. Three wires on the back of the tps sensor. Probe the top two with the key on for dc voltage. At idle it should be between .5 and 1v and at wide open throttle between 4.5-5v. Which is posative and which is negative really doesn't matter, if you get it backwards you will get the exact same reading only negative, just ignore the "-" sign and read the number. As you slide the thottle body slowly up it should be a nice continuos climb to its highest value. Mine had two spots that showed 0v where it was not making contact and one that was a dead short.

toyman · Oct 16, 2011

To clarify, the acceptable signal voltage at the closed throttle position is between .65v - 1.25v with about 1v being ideal. Within this range the PCM will learn/adapt to that signal voltage and use it as the idle base setting.

ttocs · Oct 16, 2011

is there any adjustments that needs to be done to it? I thought I saw my tuner make some adjustments on it prior to running it on the dyno years ago but the manual said there were no adjustments to be done.