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Discussion Starter · #1 ·
So I've had this issue for a fairly long time now and looking around I can't find anything to help. Ever since I had a a cheap-o exhaust job done, my Celica has had an issue where occasionally I'll get alot of rev bouncing, and every time I disengage the clutch the revs jump up as if the car was gasping for air. I initially thought it was a result of the bad exhaust job, but after replacing the ENTIRE exhaust system, the problem still occurs, especially if I disconnected the battery recently. Looking online, rev bouncing issues seem to be caused primarily by the IACV, but my car is an '03 which has DBW and thus, lacks an IACV. It almost seems as if the computer is having trouble metering the air/fuel ratio, but I have no codes and the car otherwise runs perfectly fine.

I do know I have a slight exhaust leak before the cat since the midpipe I installed didn't quite line-up right, so I have to adjust that for a start. Otherwise, all I have done to the engine was install a CAI. Everything else is very well maintained, and as far as I can tell, nothing except the exhaust is leaking. Could a slight exhaust leak before the O2 sensors really cause this issue? I may end up replacing the MAF at some point too since that's the only thing I can think of that would affect my idle.
 

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Thats going to most likely be an MAF sensor or intake related issue. Sounds like its buggin out. Clean the maf sensor and the iacv shud fix the issue.

2000 GTS Turbo
 

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Discussion Starter · #3 ·
Thats going to most likely be an MAF sensor or intake related issue. Sounds like its buggin out. Clean the maf sensor and the iacv shud fix the issue.

2000 GTS Turbo
Like I said in the post, I dont have an IACV. DBW Celicas dont need them. I will try cleaning the MAF, but I did that not too long ago, so it shouldn't have gotten THAT dirty.
 

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Like I said in the post, I dont have an IACV. DBW Celicas dont need them. I will try cleaning the MAF, but I did that not too long ago, so it shouldn't have gotten THAT dirty.
It is possible the glitch is in the throttle actuator assembly then. Did you clean the butterfly valve and thottle body? If its got dirt or grit it can hang up, then when it releases or breaks free it alows too much air to go in for that moment till it corrects it causing a blip or hunting idle.

2000 GTS Turbo
 

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Discussion Starter · #5 ·
It is possible the glitch is in the throttle actuator assembly then. Did you clean the butterfly valve and thottle body? If its got dirt or grit it can hang up, then when it releases or breaks free it alows too much air to go in for that moment till it corrects it causing a blip or hunting idle.

2000 GTS Turbo
That's a good point. Since I have a CAI, the butterfly valve has been deleted, and I cleaned the TB not too long ago as well. I'll take it all apart when I get a chance and see if perhaps I missed something during cleaning. I was also considering reinstalling my stock airbox and seeing if perhaps since it's an '03 the DBW needs the butterfly valve for some reason.
 

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That's a good point. Since I have a CAI, the butterfly valve has been deleted, and I cleaned the TB not too long ago as well. I'll take it all apart when I get a chance and see if perhaps I missed something during cleaning. I was also considering reinstalling my stock airbox and seeing if perhaps since it's an '03 the DBW needs the butterfly valve for some reason.
... i think ur misunderstanding the term butterfly valve. It cannot be deleted its what alows air in... if there was no valve or shutter the engine would be 100% WOT which isnt possible.

2000 GTS Turbo
 

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Discussion Starter · #7 ·
... i think ur misunderstanding the term butterfly valve. It cannot be deleted its what alows air in... if there was no valve or shutter the engine would be 100% WOT which isnt possible.

2000 GTS Turbo
I'm referring to the butterfly valve that comes with the stock airbox, not the throttle body's valve.
 

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Discussion Starter · #8 ·
All right, bit of an update. I finally got around to cleaning out the MAF Sensor, as well as all the EVAP Solenoids. All air hoses are new, clamps also new, everything gave a firm click when connected, and there are no engine codes. I double-checked to make sure the TB was also clean, which it was, and I even replaced the o-ring around the MAF Sensor since it looked a bit worn. Well, the issue has gotten SLIGHTLY better. The weird rev bounce doesn't happen every single time I sink the clutch, and when it does happen, it seems as if the car is now hesitant to do it. Idle and start-up also seem a bit smoother, and the engine overall seems that little bit more responsive.

I did the cleaning today, so perhaps the ECU needs time to adjust, but what I'm curious about is if this is something that all DBW Celicas do in some capacity and I just didn't notice or it's gotten more prevalent just recently. I still have that small exhaust leak, so I'll update this when I get that done to see if it helps any.
 

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Electromagnetic Wave :-h
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I'm not sure about the DBW. But, there were a few minor occasions where I ran into a weird kind of idle hunting where it ramped the IACV back & forth. REALLY annoying! The only solution for me was to shut down & restart. Basically rebooting the ECU. I haven't had this issue in a long time. With the DBW, the throttle plate is the IACV. So, make sure that the throttle is clean and that the throttle stop is adjusted correctly (often mistaken for an idle adjustment).
 

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All right, bit of an update. I finally got around to cleaning out the MAF Sensor, as well as all the EVAP Solenoids. All air hoses are new, clamps also new, everything gave a firm click when connected, and there are no engine codes. I double-checked to make sure the TB was also clean, which it was, and I even replaced the o-ring around the MAF Sensor since it looked a bit worn. Well, the issue has gotten SLIGHTLY better. The weird rev bounce doesn't happen every single time I sink the clutch, and when it does happen, it seems as if the car is now hesitant to do it. Idle and start-up also seem a bit smoother, and the engine overall seems that little bit more responsive.

I did the cleaning today, so perhaps the ECU needs time to adjust, but what I'm curious about is if this is something that all DBW Celicas do in some capacity and I just didn't notice or it's gotten more prevalent just recently. I still have that small exhaust leak, so I'll update this when I get that done to see if it helps any.
I had a similar issue years ago the revs would drop at idle I cleaned the MAF it looked fine, but in the end, it was the MAF sensor...
 

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Does the idle hunting change when you turn the heater control from Defrost down the floor? Mine does when the A/C charge is low, and the system cycles up the idle for the A/C which won't turn on because of the the low charge.
I also have noted different idle patterns from swapping in different computers. Hope this helps.
 

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Discussion Starter · #12 ·
Does the idle hunting change when you turn the heater control from Defrost down the floor? Mine does when the A/C charge is low, and the system cycles up the idle for the A/C which won't turn on because of the the low charge.
I also have noted different idle patterns from swapping in different computers. Hope this helps.
So just in case there may be a confusion as to what's happening. My revs aren't going up and down (idle hunting/surging), in those cases it usually is the IACV. However DBW (drive by wire) Celicas just don't have an IACV at all since the ECU manages idle entirely through the throttle body. Instead, what happens is as soon as I sink in the clutch, the revs jump up to between 1500-2500 rpm. How much it jumps up seems to depend on how much gas I applied beforehand, with more gas causing a larger jump. The only other issue I had was the very occasionally rough idle, but now that I cleaned everything out, it idles perfectly fine. The Defroster and A/C have no effect on idle other than a temporary slight lowering due to the increased electrical load.
 

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To be clear to anyone reading along, the IACV on these cars (00-02 models) is also controlled by the ECU. Whether it responds to commands or not is usually a cause of the idle hunt issue.
For reference to your observations, my three 00-01 GTS Celicas, my 08 Tacoma 2.7 and our 2011 Scion XD all have an rpm jump and bounce around when you are at speed and push in the clutch (like gliding in off the highway onto an off-ramp). The rpms settle down eventually when the vehicles come to a stop. Hope this helps.
 

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Instead, what happens is as soon as I sink in the clutch, the revs jump up to between 1500-2500 rpm. How much it jumps up seems to depend on how much gas I applied beforehand, with more gas causing a larger jump.
Sounds somewhat normal. I wasn't used to that either when I first got the car. If I remember back that far correctly, I was told that it was caused by the rotational inertia of the flywheel.
 

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Discussion Starter · #15 ·
Interesting, so this is indeed normal operation, that's good to know. I actually have the MWR flywheel and pullies, but it still happens with about the same intensity. Perhaps it's just a residual amount of air entering the engine after letting off the gas that gives it that slight bump in revs.
 
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