I have searched the website and cant see to find a thread that resembles my problem so let me explain and hopefully i can fix the problem.

My car was running fine for years and never had a miss or anything. I recently took it on a road trip and while on that trip it started to have a very low idle and a bad miss and sounded like it wanted to stall but didnt. The problem continued and it is still doing it. Here is what i have checked or done so far.

1. I replaced all wires and plugs and still the same miss and rough idle
2. I have replaced fuel filter and nothing again
3. I have tested the TPS and it is reading correctly
4. I have checked all fuses and all checks good
5. I have checked for Vacuum leakes and nothing is leaking

I have always maintained the car and never had problems with timing or anything but will check that today but i dont think that is the issue. Please Help before i spend lots of more wasted money on things that do not correct the problem. My SES light has not come on or ever has so it may not even work for all i know.

 

I checked the timing and it is good to go. I also started the car and then unplugged the MAF and car died so I do not think that is the problem either unless I am wrong about that observation.

I am at a loss now. Please Help

 

I would clean and check the IAC and check the fuel pressure first to rule out the IAC or fuel pump as the problem. If I had to guess though I would say its very likey bad injectors. And also remember that sometimes injectors will measure within spec on resistance but still not work correctly. Keep us posted on what you find, Good Luck!

 

Well I just did a fuel pressure check and it was steady at 45 to 47 lbs of preesure during idle and with half throttle so that can be ruled out.

I also disconnected IAC while car was running and it stalled out and died. Not sure if that means IAC is good or not.

I would like to add that the miss is really bad when engine is cold but once engine reaches operating temp then the miss is still there but not as bad. I will be checking OHMs for each injector tonight. I am not sure what to think.

 

I had a hard time getting reading last night on the injectors. Could someone please inform me what the specs should be and the proper way to test them. Thanks in advance.

 

Its best to test the injectors hot, sometimes they break down due heat and will test in spec cold and out of spec when hot. You may want to test them cold first though just because its easier with the engine cool...sometimes they test bad both ways. Disconnect the connector from the injector and put your meter(set on resistance setting) across the two metal terminals. They should measure 14-16 ohms. Anything less than 12 ohms is definately bad. Remember that this test only checks the electrical part of the injector, if its mechanically bad(leaking, sticking, clogged, etc) this check won't show it.

 

Thanks for the advice. I am cleaning the IAC now and when I am done with that I will test the injectors and let you all know the results.

 

Hi i also have a 89 iroc z28 5.7L 350 5 speed that is doing the same thing tried all the same troubleshooting (except the injectors I was told that could not be it) I did replace the MAF with a remanufactured one and still no luck. I was also told that if I got ahold of a speed density chip??(here is the part number that I found if it is the right one -) ECM1227165/ 16198259 that it would override the MAF and should solve the problem if it is not a broken wire. Would this chip help???

 

Well I checked in injectors and all were over 12 ohms. I then put throttle body back on after I removed it to remove and clean IAC module. With thoroughly cleaning of the IAC the problem was solved. Now the car runs just like before without a miss. Thanks for the advice and especially a huge thanks for this site. Without this site many of us would be lost and be wasting lots of money.