intermittent studder?

[caribougtr]

I recently bought a 92 GTR in pristine shape. That night I decided with a friend in all our infinite wisdom to wash the engine compartment. Normally this is not a issue with most cars. Now the next day when I went to drive it home 6h north the throttle would die intermittently... I would put the hammer down go through some gears and prob seemed to go away. Talked to the previous owner and he says he had no such issues so immediately diagnosed the problem to be water getting into something. Upon close inspection we found a small crack on the bottom of the ICM. The ICM sits in a recession so figure through heating and cooling of the motor perhaps through osmosis condensation got in the control board??

Does the throttle issue sound like a ICM issue? on the 6 hour drive it was good for a few hours then act up. Sometimes it acted up after I shut the motor off for 10 minutes for breaks? any help would be cool I am going out of my mind. lol


****UPDATE****

DIRTY TPS!!!! easy peazy! (word to the wise dont spray nine around sensitive stuff)

[caribougtr]

I just checked my ECU and flashing 43 TPS... any ideas? can it be cleaned?

[nelsonmxmarc]

TPS is the throttle position sensor. It's located towards the rear of the intake plenum on the metal crossmember that actuates the ITB's. Its on the furthest end from you, a small rectangular box.

Typically these things do not last. They dont take much abuse and are a common replacement part. They have a milage like 60,000km or something.. At any rate, the symptoms you describre sound very much like a TPS issue, why? TPS relays open/close throttle values to ECU. If for some reason it's on the fritz, your ecu will either adhere to open or closed throttle properties. You said it falls flat on its face for no particular reason, well the circuit is simply reading what the tps is trying to tell it (Closed!).

First, before buying a new one; pull it off and heat it with a hair dryer for 5 min. If there's any residual water left from the wash, it will dry up, and hopefuly aid the issue. Next, on the inside of the unit (the one that connects to the ITB's) is a round insert type thing. This is where the contact point of the unit is. Remember, the throttle is mechanically controlled through a pull cable; basically when you place your foot on the gas, the contacts of the tps touch the insert relaying a change in throttle to the ECU. I would clean this out as best as possible, then add a dab of dielectric grease to toughen up the contact point.

Next is setting the TPS properly. Assuming you do not have nistune or a consult, you'll need to follow the steps to set it up via a multi meter. The middle wire, WHITE, is the power wire. On a low volt reading, tap into this via the positive, and ground the negative terminal elsewhere (usually tucks into the neg on battery nicely). Read the values; at idle / CLOSED, the circuit should read ~.48, always closer to .50. OPEN is somewhere around 4.11.

If these values stand, then the TPS is in good shape.


Now.. TPS issues are common to overlap MAF issues. If the sealent on the MAF circuitry has become brittle, water may have passed, or, if you didnt properly seal your intake system, the thermisters may have become dirty/water filled.

The reason i say this is because, when people are beginning to have MAF issues, the car tends to fall on its face periodically. The reason for this is because the thermister in the maf will begin to relay different voltage values to the ECU. They work in such a way that, they heat an element, and the amount of air passing cools the element, allowing it to raise or lower voltage accordingly - up until around 5.2 volts (This is just a brief explanation on MAFS). So sometimes when they're on the outs, the tend not to heat, or heat up too much and cannot properly monitor values. In the case of my buddy TW, his car was falling on its face rather periodically. One day it'd be okay, the next, die on the highway then momentarily return to life. We noted the MAF values at idle, one being noticably higher voltage vs. much lower. We changed the lower voltage one and voila, she's good to go.

Hope this wasn't too confusing.. But if you can, pull your mafs and clean them, this may resolve your issue. If not, change your TPS if none of the above was helpful.

Good luck

[Skym]

Airleak behind MAF's can make make engine stutter (MAF gets 2 air sources instead of one). Noticeable after exiting motorway. Tightening intake hose clamp behind MAF fixes that problem. Or could be like mentioned above, some water has got past the seals on square part of one of the MAF's and causing similar symptoms or wiring, solder, etc problems.

TPS helps ECU inject extra fuel during sudden transient throttle movement to prevent engine going lean, hesitating. If TPS is adjusted wrong, ECU could be injecting less fuel causing a lean condition and hesitation or the opposite.

TPS last's about as long as o2 sensor 40-60,000km. But that depends on how you drive the car. If drive car hard it bends the WOT and idle contact pins inside TPS and wears out the circuit board track that varies the voltage. On later model Skylines they supposedly removed the idle, WOT pins and runs via looking at voltage? for idle, WOT. As far as I know, Toyota engines run a optical version of TPS, which I think is better.

[got_boost!]

Great post on it in the GTS Tech Forum in the sticky section. Everything in the post counts for the GTR as well.

[caribougtr]

Wow thanks guys!!!! son of a... this site is gonna save my life!! I will contribute more as I learn but for now am still pulling parts off cleaning and reinstalling figuring out what makes her tick!

Also on the TPS front I pulled the pot off and took it to work, put a ohm meter on er and sure enough dead spots in the reading. If I remember correct 250ohm - 10500ohm. I sprayed electrical contact cleaner into into and a nice steady flow of low pressure air. She works fine now! You guys are awesome.

Corey

[Skym]

Good to hear.