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Bad idle - Code 33/36

Old 05-13-2019, 09:38 AM
  #1  
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Bad idle - Code 33/36

I posted this in the thread for my car but thought I'd get a quicker answer here. Long story short, my car idles nicely but after running for a bit, the idle will randomly drop quickly and almost stall, then back to normal. When it drops I can give it gas and it wakes back up like there's no issue. The CEL is on, and the 2 codes are 33/36 which are MAF and burn off relay. I replaced the relay and MAF, and it had 0 effect on the idle or codes. I know the MAF works because it came out of perfectly running car, and also solved my no-start issue from a few weeks back. Could the relay be faulty, and the code for the MAF just hasn't been cleared yet?
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Old 05-13-2019, 05:08 PM
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Re: Bad idle - Code 33/36

I had issues like this and replaced everything to no avail. After I broke down and replaced the ECM, all my problems went away.
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Old 05-13-2019, 05:29 PM
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Re: Bad idle - Code 33/36

36 is a MAF code on my car but your 91 won't have a MAF it is SD.

I fixed my code 33 by replacing the TPS.
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Old 05-14-2019, 08:41 AM
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Re: Bad idle - Code 33/36

The problem's in my 89 IROC, not the 91'. I'm going to try the TPS as I've seen a few people say it's related. I have a fellow IROC owner dropping off a MAF this morning so I can see if mine's faulty or if it's another issue. I'm hoping it's a quick fix!
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Old 05-14-2019, 11:21 AM
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Re: Bad idle - Code 33/36

Code 36 is MAF burnoff failure in my 88. You fix that by replacing the burnoff relay on the firewall in front of the driver. On my 88 the burnoff relay is the one closest to the fender.

Code 33 can be set from a couple different situations. Basically the throttle position (as reported to the ECU by the TPS) and the MAF (measured airflow as reported to the ECU) are in gross disagreement. I fixed that by replacing the TPS which was the original and was worn out.

Don't change the MAF without first changing the burnoff relay. That might fix the 36. The relay is 1/10 the price of a MAF.

I bought my replacement MAF, TPS and burnoff relay from Rockauto.com. Delphi MAF, and Delco TPS and relay.

If you replace the TPS make sure you follow the instructions for calibrating the install position so you have the correct voltage at idle. it is simple but you will need a voltmeter.

Be VERY careful if you try to clean the MAF with that spray ****. I wiped out two MAFs doing that. Spray from about a foot back. the wire in the MAF is very delicate and if it gets hit from the full blast of liquid it may break.

Good luck.
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Old 05-14-2019, 12:11 PM
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Re: Bad idle - Code 33/36

Originally Posted by Tremo View Post
Code 36 is MAF burnoff failure in my 88. You fix that by replacing the burnoff relay on the firewall in front of the driver. On my 88 the burnoff relay is the one closest to the fender.

Code 33 can be set from a couple different situations. Basically the throttle position (as reported to the ECU by the TPS) and the MAF (measured airflow as reported to the ECU) are in gross disagreement. I fixed that by replacing the TPS which was the original and was worn out.

Don't change the MAF without first changing the burnoff relay. That might fix the 36. The relay is 1/10 the price of a MAF.

I bought my replacement MAF, TPS and burnoff relay from Rockauto.com. Delphi MAF, and Delco TPS and relay.

If you replace the TPS make sure you follow the instructions for calibrating the install position so you have the correct voltage at idle. it is simple but you will need a voltmeter.

Be VERY careful if you try to clean the MAF with that spray ****. I wiped out two MAFs doing that. Spray from about a foot back. the wire in the MAF is very delicate and if it gets hit from the full blast of liquid it may break.

Good luck.
I changed the BOR and haven't had a chance to clear the codes. Because it's a post running sequence, does it really have an effect on the way the car runs? I just swapped out the MAF with another one and the idle is still a bit funky. I unplugged the TPS and the car shut right off, so I know it at least "works". What about IAC? I feel like it could be part of my difficulty with the idle. When I give the car gas, the response is perfect and it doesn't try to give out. Only at idle does it fluctuate. Can't find any vacuum leaks anywhere either
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Old 05-15-2019, 10:48 AM
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Re: Bad idle - Code 33/36

Originally Posted by RKeats View Post
I changed the BOR and haven't had a chance to clear the codes. Because it's a post running sequence, does it really have an effect on the way the car runs? I just swapped out the MAF with another one and the idle is still a bit funky. I unplugged the TPS and the car shut right off, so I know it at least "works". What about IAC? I feel like it could be part of my difficulty with the idle. When I give the car gas, the response is perfect and it doesn't try to give out. Only at idle does it fluctuate. Can't find any vacuum leaks anywhere either
The TPS is essential for engine operation. I'm not surprised that it shut down when you unplugged it.

Yes, burnoff happens after you shut down the engine, and the engine has to have been running for a little while in order for it to get a burnoff. Once you do get a burnoff, the code 36 will clear itself.

When your SES light is on, the engine is running off pre-programmed tables in the ecu. That is the so-called "limp home" mode. The engine will run but not all that great. It will usually idle in limp mode just fine, at least mine has. Usually. Last time I had problems I was getting both 33 and 36 and the idle was not that good, but I know now that I also had a bad TPS.

IAC is another thing that can be looked at, which reminds me, I need to clean mine.

It is possible that you have a bad ecu. I've had to replace mine once.

I usually carry a spare burnoff relay in my console box along with the correct size nut driver and a pre-bent paper clip. If I'm out and it throws a 36, I've just changed the BOR there on the spot. Drive it briefly long enough in limp mode to need a burnoff, shut it down and wait to hear the click under the hood to know you have had a burnoff, then start up again and the code is gone.

Good luck.
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Old 05-15-2019, 11:00 AM
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Re: Bad idle - Code 33/36

Originally Posted by Tremo View Post
The TPS is essential for engine operation. I'm not surprised that it shut down when you unplugged it.

Yes, burnoff happens after you shut down the engine, and the engine has to have been running for a little while in order for it to get a burnoff. Once you do get a burnoff, the code 36 will clear itself.

When your SES light is on, the engine is running off pre-programmed tables in the ecu. That is the so-called "limp home" mode. The engine will run but not all that great. It will usually idle in limp mode just fine, at least mine has. Usually. Last time I had problems I was getting both 33 and 36 and the idle was not that good, but I know now that I also had a bad TPS.

IAC is another thing that can be looked at, which reminds me, I need to clean mine.

It is possible that you have a bad ecu. I've had to replace mine once.

I usually carry a spare burnoff relay in my console box along with the correct size nut driver and a pre-bent paper clip. If I'm out and it throws a 36, I've just changed the BOR there on the spot. Drive it briefly long enough in limp mode to need a burnoff, shut it down and wait to hear the click under the hood to know you have had a burnoff, then start up again and the code is gone.

Good luck.

I just got back from a 30 minute drive after replacing the IAC and MAF related relays yesterday. Car idled poorly and near the end of my drive, started losing power. I cleared the codes and ran the car again. Now I have just a code 33. I'm going to replace the TPS as it seems to be a common cause of the 33. We'll see what happens
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Old 05-15-2019, 11:59 AM
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Re: Bad idle - Code 33/36

Originally Posted by RKeats View Post
I just got back from a 30 minute drive after replacing the IAC and MAF related relays yesterday. Car idled poorly and near the end of my drive, started losing power. I cleared the codes and ran the car again. Now I have just a code 33. I'm going to replace the TPS as it seems to be a common cause of the 33. We'll see what happens
Replacing my TPS fixed my code 33.

Do read on the proper way to calibrate the voltage at idle, it is not hard you just need a voltmeter. I used 2 paper clips as probes to push up into the TPS connector so I could read the voltage.
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