Celica Forums General Discussion Engine and Performance 2000 Toyota Celica GT-S random power loss issue

The car on cruise control sometimes randomly looses speed & downshifts to 3 and raise rpms quickly to gain the set cruise control speed again."

Vehicle Background: bought it from the original owner, the fuel gauge showed empty on a full tank of gas and I passed on the car, owner called a week later and said they installed a used PCM and everything now works, and it did, I bought it since it was a really clean car.

After driving on highway with cruise control set it would randomly loose power and downshift and then regain speed from being set on cruise control, mostly uphills and downhills but also straights sometimes and it would loose 7-8 mphs not the 1-3 mph loss that is typical of some other cars on cruise.

Engine has been rebuilt to success, other then this issue, the car drives like a dream and doesn't burn a drop of oil. Plenty of power compared to before the rebuild as well.

I learned from a DIY oil consumption fix on a 98 corolla that removing throttle body and cleaning it and the IACV, makes the vehicle idle within stock spec, really quiet and also improves the throttle response, I attempt this on the GT-S.

So I open up the airbox to make room to clean my throttle body and the 2 nuts were fairly loose, but the 2 bottom bolts were completely out that attach the throttle body to the intake manifold and only holding their place because of the tight fit in that area from all the hoses. This wasn't even touched during the engine rebuild.

I remove everything, looks dirty as [censored] and the intake has some oil in it, which I use brake parts cleaner to dry and use air to blow off and only got to remove maybe 30% of it from the inside of the intake. I then also remove the IACV to find it REALLY dirty like all the ones I had open so far and I go to town and cleaner both that and throttle body and replace both the gaskets as well.

Upon completion the vehicle's throttle response becomes AMAZING compared to before and it seem like a proper GT-S rather then a slow car which before had a slower acceleration then my 01 GT. I drive the same route home of 25 miles, the car NEVER once down shifts and has plenty of power and I'm HAPPY!

Well guess what, the issue is back now, I open the air box and both the nuts and the bolts seems firmly tight. I loosen everything up to still see the oil in the intake(though I only got to remove/dry30% the first time), brand new OEM PCV valve in the car 5k ago and I followed the PCV Valve pipe to the intake and it was dry from the inside as well.

when the vehicle is driven around and it returns to idle, it seems to hesitate(I think not 100% since it could be the engine just slowing down didn't do it before the throttle body cleaning though) for less then a second when going back to idle speed, it idles perfectly at around 750 rpms though.

Questions:
1. What could be causing the oil in the intake? is it just the old oil what has been in the intake since before I bought it? The car doesn't burn any oil in the last 5k since the engine rebuild.

2. Could it be the PCM/VCM is causing the random power loss with cruise control on? which was a problem that was so called fixed using used parts but all the other automatic functions work perfectly.

3. Could it be the Cruise Control it self, apparently I can snag one from a local pick n pull for like 8 bucks (I think, listed on website)

4. Could it be this issue listed in this link? http://tinyurl.com/jw89s6k , bad throttle position sensor? could it be that I cleaned the idle air control valve too roughly to get that slight hesitation when returning to idle?

5. Could it be the Throttle body itself in the GT-S? Did I clean it too aggressively, and ruined the round opening, which is causing the random loss of power? I had my cuzin do the throttle body removal and cleaning DIY step by step on our 99 corolla and he used a gasket remover (attached to a power tool) to clean up the dirt/oil build up inside the round opening and it started to give him jerks driving at highway speeds, constantly...We used the 98 corolla's gently cleaned throttle body in the 99 corolla and immediately issue solved. The proper working throttle body in the 98 corolla is a used replacement one as I aggressively cleaned the round opening in the original one and had hesitation issues as well.

I would really appreciate any input as this is annoying and because replacing all these parts which might be unnecessary and will end up costing a fortune.

Update(1.0): seems to be a faulty MAF sensor(it didn't trigger a CEL), by replacing it with a re-manufactured Cardone sensor (I made sure it was a Denso Sensor) it fixed the issue temporarily but the issue came back once.

Note: the old "maybe faulty" MAF Sensor's rubber o-ring was deformed/stretched and most likely not sealing.

Then I used a junkyard MAF sensor(very very dirty) from another celica, cleaned it really nice with CRC MAF sensor cleaner(I do this on all my MAF sensors as a maintenance) and installed it. So far no issues, I will have to drive it more to confirm.

Update(2.0): 500 miles since the junkyard MAF sensor replacement, and the 302 highway miles that were observed didn't see a single power loss issue during cruise control, where before it was experienced specially at 65+ mph(randomly), this will be my last update as the issue seems fixed, unless the issue arises again.

Note: the faulty MAF sensor, never triggered a CEL, which could also indicate it might have been just the rubber o-ring($0.99-5.50ish from Toyota dealer), it was so elongated and deformed, most likely from a prior improper installation of the MAF sensor.

Thanks to Smaay and Bitter for both suggesting the first thing I look at should be the MAF sensor and it turned out to be that exactly. These guys are absolutely awesome.

Update(2.0): LOL MAF sensor replacement didn't do anything, the issue came right back, I ended up selling the car for it's awful fuel economy because of it's 4 speed auto mated to the 2zz-ge engine.