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Could somebody post some links to past threads that get into the details of how to check the voltages the MAF should have along with the burn off relay? I know I read something a while back & I cannot seem to find it. My 87 has had cold start issues for ever that I have just lived with & earlier this summer I decided to adjust the throttle blades using the parking brake method. After doing this (and finding my blades were set too far open) my car now throws a code #34 "sensor or circuit too low" For testing purposes I installed the MAF sensor from my GTA & nothing changes, so the MAF sensor is fine. I'm suspecting its something in the wiring, relay, or the ecm itself. Here's a screen shot of what I am seeing on the scanner. This is at a cold start & why the iac counts are so high & coming down.
Airflow started & stayed right at 4 even though the RPM was going down after the 1000rpm cold start. Thinking this has something to do with it.
Any links towards info I can read up on would be appreciated, Thanks!
Last edited by F-body-fan; 09-24-2022 at 09:14 AM.
Backing up a step, when setting the throttle plate position (minimum air position) the engine needs to be at full operating temperature, IAC fully closed and disabled, and TPS voltage continually adjusted to maintain the average 0.54VDC (±0.08V). Most importantly, a reliable tachometer needs to be used, That means the in-dash thing is not suitable for this, and data link software is not always suitable for this. Something reading the actual switched output to the ignition coil primary falls into the "reliable" category.
Second, MAF raw output voltage is a reasonably linear voltage dependent on air flow through the instrument. The lower flow ranges are highly sensitive. Since the voltage signals are so low, any resistance would have a greater affect on the low range (idle speed) readings. That's why clean and reliable connections are a necessity in the MAF system, including those within at and the relays, the wire harness connectors and splices, and the ECM connections. Of course, that always includes reliable grounds for the 12V and 5V systems.
The ECM uses lookup tables for the acceptable ranges of air flow at a given throttle angle (heavily reliant upon correct TPS voltage) and given RPM (as seen by the ECM). These can be affected by modifications including a gutted MAF sensor (turbulence screens removed), a different cam profile from stock, altered intake tract, and variations from stock valve and ignition timing.
If may be possible to "band-aid" a low MAF range error by adjusting the TPS voltage to near the minimum allowable setpoint of 0.48V. That would force the ECM to skew the allowable range of MAF signals downward and could potentially remedy the problem. If the timing, idle RPM, and minimum air are correct, that may be one of the few easy steps to try.
Thank you for the added info! I believe it was your write up I followed to set the blades. loop was closed, but I waited until the fans were kicking in,
then closed the iac & disconnected the ign advance. I was surprised how far I had to open the blades to even get it to idle! I had set them in the past
by using the iac steps. After going through the procedure this seemed to cure the decades long problem I have had with this car for as long as I can remember. But now it throws the 34 code right after I start it. In fact, I just realized it throws the code before I even start the engine! So this should not be too hard to figure out, I just didn't know what wires are what on the connector to put my meter on for the 12V & 5V.
What is interesting though is, right now its starting & idling smoother than it has in forever even though its throwing the 34 code. the ECM is seeing 7 at idle from the MAF & it does seem to double with the RPM, so it appears to be getting a good signal, Does 7 seems close, or is that too high/low?
I did not check the relay yet, I'll have to research that procedure. Kinda funny, my solus shows if the maf burn off is active, however seeing it happens after you turn off the key, I am not sure how it would read anything but off.
Anyway, Car is completely stock with exception to the muffler. stock replacement, not aftermarket performance. I have owned this car for just about 30 years now. ITs been doing this first start idle stumble for as long as I can recall, so every once in a while when I get the car out, I try to figure out why it does this.
wire connectors at the maf look fantastic, although that doesn't mean something isn't compromised, just look good visually.
I started over, reset blades to 500rpms following the posted procedure. set the TPS at .48v no change, in fact seem to idle a bit rougher.
iac counts are close to zero & jump to 4 +/- in gear MAF now is down to 4. Weird that the maf would drop to 4 at the same rpm that was reading 7 before? Still setting code 34 within a few seconds of starting the engine.
Stangest part about this is it did not start setting codes until I had went through the procedure above. last week I slowly closed the throttle blades & watched the iac counts climb to compensate while adjusting the tps each time. small changes each time, but it seemed to like the blades a bit more closed with a higher iac count. Also my solus can not reset the codes anymore. I have to disconnect the battery. Thats something new.
While I know ecm's don't fail often, I wouldn't mind trying another one.
09-24-2022, 09:10 AM
