Code 33 - possibly caused by bad TPS?
Thread Starter
Drifting
Joined: Mar 2017
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From: Nashville TN
2017 C4 of Year Finalist
Code 33 - possibly caused by bad TPS?
I’ve recently started having a code 33 issue on my 1985 manual Corvette. It’s been intermittent but getting much more frequent to the point that I need to deal with it before I can trust the car.
A few points:
What is a good way to test the TPS? I understand you have to check voltage, I don’t want to tear up my wiring harness. Any tricks how to do this?
I will do the FSM MAF procedures as well, but TPS is an easy replacement if we think that’s a likely culprit. Also, any good non-FSM tests to try first? I really don’t want to have to dig through the dash if it can be avoided.
thanks!
A few points:
- when code is thrown, it runs like garbage up to 1/4-1/2 throttle, like I’m not even pressing the pedal. Then suddenly around 1/2 throttle it picks up again. This threshold seems to vary slightly leading to severe jumping.
- The issue seems more prevalent after the car is warmed up
- the issue can come and go WITHOUT stopping the car/turning off ignition. It runs like crap for 5 minutes then suddenly is fine, even with CEL on.
- I’ve also had a surging idle in the past, though it has been very minor recently and on its own not terribly concerning.
What is a good way to test the TPS? I understand you have to check voltage, I don’t want to tear up my wiring harness. Any tricks how to do this?
I will do the FSM MAF procedures as well, but TPS is an easy replacement if we think that’s a likely culprit. Also, any good non-FSM tests to try first? I really don’t want to have to dig through the dash if it can be avoided.
thanks!
Le Mans Master
Joined: Aug 2017
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From: New Jersey
I can't comment on if it could be caused by a faulty TPS.
That being said to test it I use needles or something long and thin to back probe the connector through the weatherpacking and then just test the voltage as you move the pedal. It should be a smooth sweep up to around 5v from whatever your specified FSM adjusted base voltage should be.
The needles slip between the weather pack and wire and when pulled out put the seal right back with no damage occurring.
That being said to test it I use needles or something long and thin to back probe the connector through the weatherpacking and then just test the voltage as you move the pedal. It should be a smooth sweep up to around 5v from whatever your specified FSM adjusted base voltage should be.
The needles slip between the weather pack and wire and when pulled out put the seal right back with no damage occurring.
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
Likes: 165
From: Nashville TN
2017 C4 of Year Finalist
I can't comment on if it could be caused by a faulty TPS.
That being said to test it I use needles or something long and thin to back probe the connector through the weatherpacking and then just test the voltage as you move the pedal. It should be a smooth sweep up to around 5v from whatever your specified FSM adjusted base voltage should be.
The needles slip between the weather pack and wire and when pulled out put the seal right back with no damage occurring.
That being said to test it I use needles or something long and thin to back probe the connector through the weatherpacking and then just test the voltage as you move the pedal. It should be a smooth sweep up to around 5v from whatever your specified FSM adjusted base voltage should be.
The needles slip between the weather pack and wire and when pulled out put the seal right back with no damage occurring.
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
Likes: 165
From: Nashville TN
2017 C4 of Year Finalist
TPS voltage seemed good. I ran through the FSM procedure and all the voltages on the harness were good-which indicates the MAF. The only thing is, that it had been intermittent.
I had another MAF sitting around from a parts car (that thing has been worth every penny) and so I swapped that in and went for a drive. No issues, no hesitation, just pure power and fun. I'm going to give it a few weeks of around-town trips, however, before I call it good for a cross-country road trip. Which is too bad, because it's my tenth anniversary and we're going for a weekend in the mountains and it would've been perfect. Ah, well.
I had another MAF sitting around from a parts car (that thing has been worth every penny) and so I swapped that in and went for a drive. No issues, no hesitation, just pure power and fun. I'm going to give it a few weeks of around-town trips, however, before I call it good for a cross-country road trip. Which is too bad, because it's my tenth anniversary and we're going for a weekend in the mountains and it would've been perfect. Ah, well.
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
Likes: 165
From: Nashville TN
2017 C4 of Year Finalist
Originally Posted by IHBD;[url=tel:1605409959
1605409959[/url]]Code 33 is MAF. Not TPS.
Your symptoms sound very similar to my 85 when it was setting Code 34, which is the other MAF code. I eventually replaced the MAF after it shot craps altogether and was undrivable. No more MAF codes in the 20 years since.
Take the car on your anniversary trip. Carry the take-out MAF as a spare. If you have trouble, you can go back to the old MAF that usually clears up. But I think you'll be fine with the parts-car MAF.
Your symptoms sound very similar to my 85 when it was setting Code 34, which is the other MAF code. I eventually replaced the MAF after it shot craps altogether and was undrivable. No more MAF codes in the 20 years since.
Take the car on your anniversary trip. Carry the take-out MAF as a spare. If you have trouble, you can go back to the old MAF that usually clears up. But I think you'll be fine with the parts-car MAF.
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
Likes: 165
From: Nashville TN
2017 C4 of Year Finalist
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Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
Likes: 165
From: Nashville TN
2017 C4 of Year Finalist