RKeats

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?

M G Brewer

I had issues like this and replaced everything to no avail. After I broke down and replaced the ECM, all my problems went away.

Tremo

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.

RKeats

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!

Tremo

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.

RKeats

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

Tremo

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.

RKeats

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

Tremo

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.

RKeats

So little update on my issues. I changed the TPS, IAC, and both MAF related relays, then cleared the codes. Car would run fine and now codes popped up, but the idle was pretty rough. I adjusted the TPS to .54, and did the proper reset on the IAC, and it made almost no difference. The car accelerates perfectly, and no hesitation at any level of throttle, it's just the dead idle that's bad. Maybe I have to set the minimum idle with the idle screw, but why would that need to be adjusted if it's never been changed since factory? It still has the cover over it (which I don't know how to take off either)

firefox7518

I had the same thing. I ended up measuring the injectors and checked them for big differences and low ohm ones. I had a variety of different ohm results ranging from 8 to 16 ohms which was enough for me to change them last weekend. My idle is now rock stable and this blips and stumbles it had went away. I propose that you measure your injectors cold and after a longer drive. Everything below 10 ohms should be a reason to change the injectors in my opinion. I just used the cheapest ones I could found on Rockauto, I believe they were Standard Motors Products injectors :-) I'm in the middle of building my 355 with First TPI and Trickflow Heads so I don't want to invest a lot of money for the old tired engine. It's funny how a stable and good sounding idle can fix the love to a car, haha

RKeats

I actually measured mine last night quickly and got some odd readings. One was 6, one was in proper range (16 or so), and the other 6 were between 20-21. I'm ordering SouthBay ones today as clearly they're faulty. What would happen to injectors to make them read above 20 ohms??

Tremo

Yeah, if idle still sux, and you have the MAF and related stuff working, then the next thing I'd look at is injectors.

Tremo

When was the last time you changed the fuel filter? Have you measured your fuel pressure at idle?

What shape are your spark plugs in?

RKeats

I don't have a gauge so I can't say what the FP is. I also haven't had the car long so I can't say when the plugs were done, and I haven't had a chance to check. The wires look fairly new so I'm guessing the plugs arent ancient

Tremo

Don't "guess". Know. Find out.

RKeats

Haven't had a chance to pull a plug yet, but I know for sure that at least one injector is down as it only reads 6. Am I wrong by thinking that one down injector will give me a bad idle but remain "drive-able" under acceleration?

firefox7518

As I recall its running as long it is just one which is that bad. As soon as there two really low ohm ones the current draw is too high and the whole bank is dead. I had two below 10ohms and it was running ok above idle but the idle was just rough and not really smooth.

RKeats

Similar to mine. I can accelerate decently, though there's definitely a lack of power. When it idles though it comes very close to stalling sometimes, and sounds like it's missing

RKeats

Just wanted to give a quick update. Replaced my injectors as they all read off, and the idle is way better. One injector body was actually broken so it started leaking everywhere, but on the brief drive before it started leaking, it seemed to drive very well.

Tremo

Sheet, I probably need new injectors. I'm still running the originals from 88.

RKeats

Yep, I think your time has come. They're fairly cheap from Southbay. Definitely worth the swap