2000 Toyota Celica GT-S Issue

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Laramie, WY
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.
 
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4,597
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Vent yr PCV to atmosphere, clean the TB again, disconnect the battery for half an hour or so and then go through the relearn idle procedure. If the issue persists replace the tps. Assuming, of course, that you have ensured there are no vacuum leaks anywhere.
 
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War Eagle
Some vehicles, like my old 2000 vw 1.8 turbo have exhaust gas recirculation that comes on while engine is cold to reburn the exhaust gas to aid in emissions. This might dump some unburned oil back into the intake and cause buildup. I don't know if your car has it but you might investigate. And like olas stated, check all hoses and connections for cracks and loose joints.
 
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OVERKILL

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Originally Posted By: Olas
Vent yr PCV to atmosphere, clean the TB again, disconnect the battery for half an hour or so and then go through the relearn idle procedure. If the issue persists replace the tps. Assuming, of course, that you have ensured there are no vacuum leaks anywhere.
Why would you be advocating he vent his PCV to the atmosphere? That's just negligent pollution. Installing a catch can to deal with the oil mist/blow-by products is the proper way to do it.
 
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Originally Posted By: OVERKILL
Originally Posted By: Olas
Vent yr PCV to atmosphere, clean the TB again, disconnect the battery for half an hour or so and then go through the relearn idle procedure. If the issue persists replace the tps. Assuming, of course, that you have ensured there are no vacuum leaks anywhere.
Why would you be advocating he vent his PCV to the atmosphere? That's just negligent pollution. Installing a catch can to deal with the oil mist/blow-by products is the proper way to do it.
I advocate his PCV be VTA'd because he state the TB is getting dirty - assuming adequate air filtration the TB should be spotless, so it's partly to do with engine cleanliness. Second, with a catch can in place the oil and water vapour may be caught, but there is still a volume of oxygen free gas entering the intake and displacing atmospheric, oxygen rich air. This has the effect of decreasing the overall volume of combustible inlet charge and reducing the effective swept volume of the engine. This is before we get into the effect of oil vapour reducing octane levels. Ultimately, an SI engine wants atmosphere and fuel to be happy, it doesn't want to have to rebreathe exhaust gas, water or oil vapour. More succinctly, a system devoid of compromise is closer to being optimised.
 

OVERKILL

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Originally Posted By: Olas
Originally Posted By: OVERKILL
Originally Posted By: Olas
Vent yr PCV to atmosphere, clean the TB again, disconnect the battery for half an hour or so and then go through the relearn idle procedure. If the issue persists replace the tps. Assuming, of course, that you have ensured there are no vacuum leaks anywhere.
Why would you be advocating he vent his PCV to the atmosphere? That's just negligent pollution. Installing a catch can to deal with the oil mist/blow-by products is the proper way to do it.
I advocate his PCV be VTA'd because he state the TB is getting dirty - assuming adequate air filtration the TB should be spotless, so it's partly to do with engine cleanliness. Second, with a catch can in place the oil and water vapour may be caught, but there is still a volume of oxygen free gas entering the intake and displacing atmospheric, oxygen rich air. This has the effect of decreasing the overall volume of combustible inlet charge and reducing the effective swept volume of the engine. This is before we get into the effect of oil vapour reducing octane levels. Ultimately, an SI engine wants atmosphere and fuel to be happy, it doesn't want to have to rebreathe exhaust gas, water or oil vapour. More succinctly, a system devoid of compromise is closer to being optimised.
And if we were talking about an off-road drag car where we are working on shaving every 10th of a second possible off ET and maximising MPH and not a DD where removing emissions equipment is illegal, sure. But we aren't. A catch can will likely solve the TB getting dirty issue and is still emissions compliant. There are HUGE fines up here for doing what you've suggested and the MTO does in fact do random roadside stops.
 
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Huge fines and random roadside stops don't sound I've much fun, over here we have an annual road worthiness inspection which includes an emissions test, but only tailpipe emissions. HC & CO are what counts, the numbers vary on the age of vehicle. Ting is, these numbers are lower with VTA as opposed to recirc, which gives more scope for cam overlap and exhaust scavenging. I'm not a racer, just talking from the experience of tweaking my own motor - started off as an attempt to reduce the frequency with which I had to strip and clean carbs, and a little reading showed me a whole load of other benefits.
 

OVERKILL

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Originally Posted By: Olas
Huge fines and random roadside stops don't sound I've much fun, over here we have an annual road worthiness inspection which includes an emissions test, but only tailpipe emissions. HC & CO are what counts, the numbers vary on the age of vehicle. Ting is, these numbers are lower with VTA as opposed to recirc, which gives more scope for cam overlap and exhaust scavenging. I'm not a racer, just talking from the experience of tweaking my own motor - started off as an attempt to reduce the frequency with which I had to strip and clean carbs, and a little reading showed me a whole load of other benefits.
The '85 Mustang my buddy used to own that I put the engine together for had a scavenging system on it (installed by the previous owner) that connected the valve cover vents to the collectors on the headers. This creates a slight negative pressure in the crankcase (kind of like a poor man's vacuum pump), which increases ring seal. A lot of the guys that I used to drag race with had VTA, a vacuum pump or something else, as the blow-by with 18+PSI being fed into the intake would result in a lot of oil mist entering the intake tract and with boost that's a recipe for detonation due to the lowering of the octane. These cars of course have no knock sensor so keeping true to the tune is paramount. That said, most of the road-going cars are kept emissions compliant, which, in the US and Canada, means having your factory emissions equipment, or CARB-compliant replacements fitted to the vehicle. This is often where you'll see a catch can type setup fitted to aide in keeping the intake tract clean, whilst still retaining the required PCV/breather function. After what my one friend went through in fighting a catalyst refit with the MTO, which involved a huge fine and a court date to fight said fine and several months of dealing with that nightmare (and he's a registered mechanic who was very familiar with the emissions testing rules) I would never advocate anybody in a place where a visual inspection could result in that type of penalty to modify their factory emissions equipment. It just isn't worth it.
 

AKhan87

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Originally Posted By: Olas
Vent yr PCV to atmosphere, clean the TB again, disconnect the battery for half an hour or so and then go through the relearn idle procedure. If the issue persists replace the tps. Assuming, of course, that you have ensured there are no vacuum leaks anywhere.
No intention to make any modification, TB didn't have oil after I cleaned it, only the intake did, it seemed to be old oil from before cleaning (I think) I explained the PCV and its hose being new and dry inside because I wanted to eliminate that as a source of oil, unless there is another way to get oil into the intake. From your explanation a faulty TPS could be it, also in 4th gear even driving without cruise control, it rarely but rarely does seem less responsive the usual, so I wonder if the round in the throttle body is off spec. By the way there is a really skinny hose that runs from the intake manifold (assuming it's air only) to the Airbox and it attaches to something called "butter fly valve" (source Celica forums) not referring to the butterfly inside the TB of course. On Celica forums people removed it to get better responsiveness but also a louder engine(doesn't sound tempting to me), behind the valve leading into the Airbox where on top the air filter sits, was moist (oily) and I have never seen that in a car, I cleaned up the first and sprayed brake parts cleaner which dried it up (this tell me it was oil), this area was kind of moist on my second removal even after I dried it off the first time.
 

AKhan87

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Update: 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 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.
 

AKhan87

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Another Update: 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,.
 

AKhan87

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Another Update: all the attempts were pointless and a waste of time, whatever basic things that could have been changed were done in an attempt to fix this and nothing worked, sold the car, it was awful performance (4 speed auto instead of the 6 speed manual) and it was terrible gas mileage and required premium gasoline only. Bought a 00 celica gt instead as I love my wife's 01 celica gt for its sufficient power & great gas mileage for a old car.
 
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Originally Posted By: 01_celica_gt
Another Update: all the attempts were pointless and a waste of time, whatever basic things that could have been changed were done in an attempt to fix this and nothing worked, sold the car, it was awful performance (4 speed auto instead of the 6 speed manual) and it was terrible gas mileage and required premium gasoline only. Bought a 00 celica gt instead as I love my wife's 01 celica gt for its sufficient power & great gas mileage for a old car.
Originally Posted By: The_Eric
Most common causes- aftermarket cruise units (junk) and (if equipped) vacuum servo.
Did you ever check out the vacuum servo that runs the cable to the throttle body? Seems like you checked into a lot of more complicated stuff that's less obvious. While not common, it's not the first time I've seen a failing servo do the exact thing yours was doing.
 

AKhan87

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Originally Posted By: The_Eric
Originally Posted By: 01_celica_gt
Another Update: all the attempts were pointless and a waste of time, whatever basic things that could have been changed were done in an attempt to fix this and nothing worked, sold the car, it was awful performance (4 speed auto instead of the 6 speed manual) and it was terrible gas mileage and required premium gasoline only. Bought a 00 celica gt instead as I love my wife's 01 celica gt for its sufficient power & great gas mileage for a old car.
Originally Posted By: The_Eric
Most common causes- aftermarket cruise units (junk) and (if equipped) vacuum servo.
Did you ever check out the vacuum servo that runs the cable to the throttle body? Seems like you checked into a lot of more complicated stuff that's less obvious. While not common, it's not the first time I've seen a failing servo do the exact thing yours was doing.
vacuum servo? I would have to trace that, even the first time I had no idea what you were talking about...its a vacuum line that should be at the beginning of the throttle cruise control cable?
 
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If you follow the cruise control cable back from the throttle body, it will likely end at a device that has electric and vacuum going to it. It could be all electronic, but it seems most imports in that era had those vacuum servo jobs. Anyway when they fail, that's one of the things it will do. drop, then pick it back up. Hold it for a while, then drop it again and pick it back up moments later.
 
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I see. In that case, I wouldn't have been surprised to see that it was a faulty speed control box- the part the cable goes to.
 

AKhan87

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Originally Posted By: The_Eric
I see. In that case, I wouldn't have been surprised to see that it was a faulty speed control box- the part the cable goes to.
Cruise control unit itself? I asked a lot of Toyota people on 3 different forums and the local Toyota tech I know, all said they highly doubt it, so I let it go.
 
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