Code 42 on a 92 rs starting, driving and idling problems

Ok, I'm working on a 92 RS for a friend of mine. The car has, needless to say... problems! Originally, she took it to a shop and they ran codes on it got the code for o2 sensor and replaced it. That did absolutely nothing to fix the problem. Then she contacted me and I looked at it. It will start (though it seems the solenoid is going out... click click anyone?) when it is running cold the ide jumps between 0 (when it dies of course) and about 1300 rpms. When warm it does basically the same thing but will run a little longer without throttle. I drove it around and found no power till 2500 rpms, won't downshift on its own from the throttle (ie: accelerating and flooring it wont make it downshift, I think from lack of power or vacuum?), after 2500 prm's it goes, but not too fast. With lack of knowledge about these cars I figured start swappin parts and changed out the dist cap first. All wires are where they should be now, as before. That did not fix the problem, so yesterday I look at it again and the vacuum for the heater valve was off, put it on and the heater valve cracks (from just touching it), then as I'm looking further down into the engine bay I notice the air injection tube from the smog pump is completely disconnected! I bolt it back up and the car runs better, but is now getting a trouble code of 42, electronic spark timing..... I know nothing about this as I drive an older f***. (Hey, at least it's american :) ) So, where do I need to look for fixing this problem?

code 42 is set when the one wire feed from the ECM to the distributor is disconnected. The distributor is electronicly controlled for advance and retard based on engine sensor data. While it does sound like it has several problems, i ould say that the inline connecter has been unplugged, and the distributor has no adjustments. Before you do anything, try to find this connector. It is a single orange wire that runs along the passenger side firewall, it should be about halfway between the distributor and the passenger side fender. if it is unplugged, do this before you plug it in. use a timing light to check your current timing, or base timing with the distributor disconnected from the computer. It should be 0 degrees. now turn off the engine, and connect that wire. and start it up again. It should be running better.

Other possible problems could be the Idle Air Control Valve,

the Ignition Control Module.

and probly the air injection system, if its not working, then the engine will be running rich according to the O2 sensor, and it will lean itself out, killing power.

Ok, thanx for the advice. I will check the wire. As far as the other 2 parts go, the idle air control valve and the ignition control module, where exactly are the 2 of these mounted? I was thinking, the ide air control valve, that wouldn't affect straight driving, or acceleration would it? Another thing the car does that I forgot to mention, won't idle in Drive at a stop without applying gas, or if it does only when it is warm and does not idle well at all. When shifting from park to drive it is difficult (to say the least) to keep the car from dying before you can get going. When accelerating from 0 you have to pump the gas to keep it from dying. At idle, floor it in neutral and it bogs down and dies also. Also it does seem to be lacking power at all rpms, enough so that when you floor it to accelerate, unless you are manually shifting it, it doesn't down shift at all.

http://files.automotiveforums.com/gallery/watermark.php?file=/503/146920tbiunit1.jpg

That is your Idle air control valve

To get to your ignition control module, you haveto take off the dist. cap and rotor.. A bad ignition module will also throw a code 42.. After you've confirmed the dist. advance is hooked up, the ignition module would be the first thing i checked/replaced

thank you, I will check those asap

yup, now that you mention those additional symptoms, it sound a hellluva lot like the ICM. its less than 50 bucks, or it was when i bought one. and easy to intall. Damone is correct in that its under the cap, and actually right below the rotor. It will be a black module held down by two screws, and should have three electrical connectors on it.

Damn, did it all and no luck. I replaced the control module, the idle air control valve, the dist cap, checked for the wire (could not find, but no loose or disconnected wires on firewalll or near distributor),lets see what else, replaced the map sensor, did a vaccuum leak test, I can't check the timing right now dont have cant afford :( a timing light at the moment. I did find some more interesting things to write about though :) . While trying to figure out how to get this thing running enough to drive it, I unplugged the vaccuum line from the map sensor.... Wow! what an improvement, the cars idle evened out, you could floor it and it wouldn't die, even drove it and it almost ran perfect, minus some power and other problems ie: still had a bit of trouble getting going in first gear. However the car would now downshift, would still die sometimes also though. What else... after the car got thouroughly warmed up it became impossible to get it started and running again, tried plugging the vacuum line back in, no luck, unplugged the harness to the map sensor, no luck. It eventually starts but takes so long the starter is going to burn up. Of course with map vac unplugged check engine light comes on which is of course when the idle finally evens out (takes about 5-10 secs of running time) which leads me to believe that is the problem with starting it when it is fully warmed up. When it does start vac unplugged you have to pump the crap outta the gas to keep it running till that check engine light comes on. *Sigh* Lets see, also ran codes again, 42 is gone now, and of course playing with the map sensor gave it a 33 and 34 code (map sensor voltage codes) but it also pulled a 12 (everything ok I think right?) and a 44, lean condition detected. Shouldn't this thing run full rich when that vaccuum is unplugged?....................................... I can't think of much else, sorry if this seems a bit jumbled, just so much to say. I don't want my friend to have to go out and buy another car (sshe's looking at a grand am.... I have one, and though it runs perfect, its the biggest pain in the a** in the world to work on.) she has a nice camaro after all... hopefully you guys can help me track this problem down. Thank you in advance!

replace the map sensor, sounds like thats where the problems converge.

I tried replacing the map sensor and the problem was still there...... Any other ideas?

sorry, no more without actually having it there to look at. im out of internet diagnostics.

ignition coil

Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.

During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.

An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.

The conditions for setting this code are:

System in BYPASS mode but the ignition module is still controlling timing

- or -
Engine speed > 600 RPM with no EST pulses (ECM controlled timing) going to the ignition module for 200 msec.



Typical causes for this code include:

1) BYPASS line is open or grounded
2) EST line is open or grounded
3) PROM or CALPACK not seated properly in the ECM
4) Poor connections between ignition module and ECM
5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
6) Faulty or incorrect ignition module
7) Faulty ECM


If you disconnected your map and it ran better, I would check your PROM. If the computer does not get a MAP signal, it will read off the CALPAK (small chip) which is the limp home mode. It contains all the vital info for the engine to run. The PROM (big chip) does all the fine tuning.

Thank you Hypsi, and everyone else. Ok, the PROM, I take it that is the main chip for the computer in the car? Is there a way to check it without having to buy a whole new computer? Also, just a theory and I don't know that much about cars but when I unplugged the vacuum from map car ran almost perfect. With vac unplugged I also unplugged the wire harness from map, car died almost immediately. If there truly was a problem in the ecm, when I unplugged the vac from map and it ran good, makes me think the computer is not bad but something related to the map sensor or something that works in conjunction with it is bad... problem is I have no idea what that may be or how to go about figuring it out. Im sure the computer works in conjunction with it, but is there nothing else? The reasoning behind this theory and I don't know exactly how this works, but this thing is electronically controlled timing? and with the map vac unplugged, the timing was obviously near or right on where it needs to be because the car was running right on all rpms. Also, and this is the order of replacement, Dizzy cap first with rotor, then rehooked up the smog pump, neither helped at all... replaced the ICM, very little difference there, the IAC, again little difference (though both of them being replaced did seem to help a bit, it ran just a hair better) and up till now have not run anymore codes. By chance I found the MAP sensor and unplugged the vac line, and WALAH!, it runs better. Thought we had the problem temporarily fixed, but after it got hot and we shut it off could not get it to restart. Replugged the map sensor and no start, so we ran codes at that point (which of course brought the 33 and 34 codes right off the bat) and also got the 44 code lean condition detected. 12 was also there... thats the ok code I think.... thanks for your help..... *sigh* LOL

Thank you Hypsi, and everyone else. Ok, the PROM, I take it that is the main chip for the computer in the car? Is there a way to check it without having to buy a whole new computer? Also, just a theory and I don't know that much about cars but when I unplugged the vacuum from map car ran almost perfect. With vac unplugged I also unplugged the wire harness from map, car died almost immediately. If there truly was a problem in the ecm, when I unplugged the vac from map and it ran good, makes me think the computer is not bad but something related to the map sensor or something that works in conjunction with it is bad... problem is I have no idea what that may be or how to go about figuring it out. Im sure the computer works in conjunction with it, but is there nothing else? The reasoning behind this theory and I don't know exactly how this works, but this thing is electronically controlled timing? and with the map vac unplugged, the timing was obviously near or right on where it needs to be because the car was running right on all rpms. Also, and this is the order of replacement, Dizzy cap first with rotor, then rehooked up the smog pump, neither helped at all... replaced the ICM, very little difference there, the IAC, again little difference (though both of them being replaced did seem to help a bit, it ran just a hair better) and up till now have not run anymore codes. By chance I found the MAP sensor and unplugged the vac line, and WALAH!, it runs better. Thought we had the problem temporarily fixed, but after it got hot and we shut it off could not get it to restart. Replugged the map sensor and no start, so we ran codes at that point (which of course brought the 33 and 34 codes right off the bat) and also got the 44 code lean condition detected. 12 was also there... thats the ok code I think.... thanks for your help..... *sigh* LOL

ok im sorry, I though you unplugged the harness. well with the MAP vac suppply unplugged, the car will think it is under full load so it will richen up the fuel mixture by quite a bit... just out of courisorty, do you have a way to check your fuel pressure? If so do that and tell us what it is.

Oh thank goodness, I thought there might be some way that calpak could make the car run almost perfect with that vac line unplugged. I dont have a way to check the fuel pressure besides visual (which won't do any good) being that it is a throttle body application. It looks to me like it is squirting just fine, but visual is probably not much of an indication. If i had to pick up a tool to measure it what would I need and an approx price, though I do have a compression tester not that I can use that. Fuel filter is new by the way, but maybe the fuel pump is having problems or is there a regulator or or or? Thanks a bunch for all the help though.

hey yall, I just wanna say thanks for all the advice.....I have learned so much reading all the diagnostic info, and a special thanks to oxygenatedWiring - he rocks with his patience in working on my car!