So my '93 6 speed has been running really well recently (finally). Last night after a short highway cruise, the CEL comes on for a few minutes then turns off. A short while later, it comes back and stays on until I get home 20 minutes later. The entire time the car still ran fine, no major issues. I haven't pulled the codes yet (autozone was closed by the time I got back) but I did notice a loud popping noise from the (factory) exhaust when I would back off the throttle after acceleration, almost like a backfire but not quite the same. I will usually get the some popping sounds from the exhaust under normal conditions, but they got much more frequent and louder after the CEL came on which is why I think they may be related. Manifold gaskets and cats are new. Obviously, I'll know more after I pull the codes tonight but, on a preliminary basis, does that sound like anything anyone has dealt with before? I'm thinking O2 or maybe a MAF issue could be the culprit but I'm not sure. I'll post the codes tonight, but if anyone has initial thoughts, I'd be interested to hear.
Thanks!

Doug

 

Do a search on how to pull the codes with a paper clip.
Just a guess is something in the EGR system since it comes on at highway speeds.
I've got to fix my vaccum lines or clean my 2 year old EGR valve cause mine comes on now.

In the past I had a knock sensor code that would come on soon after start up and then go off. Last maintenance I put in new knock sensors and have not had that intermittent code again.

 

Any attempt at diagnosis w/o codes is a shot in the dark. On driveability issues, the code(s) will head you in the right direction.

 

i had no idea about pulling codes with a paperclip, that's really interesting.
It was throwing code 32 maybe three or 4 months ago, so I had the EGR valve replaced with no CELs since until last night. I guess it could be a vacuum line or maybe the new valve is junk...

 

Yeah i hear you, and i'll post what i pull off the scanner (or paperclip) tonight. I just though someone may have had similar problems in the past and could give me an idea of what to expect.

 

Just use a hand vaccum pump and see if the rod moves.
I'll be doing that tonight as I get the 92 ready for emissions testing.

 

ok so i pulled H25, H23, H64 and H61 and i have no idea where to find out what those mean lol. did a search for a list, but didn't see anything...

edit: found a list. 25 and 23 are air intake temps high and low. 64 was the O2 and I couldn't find 61 but im guessing thats the other O2

 

Codes 23 and 25 both indicate out-of-range readings in the IAT (Intake Air Temp.) sensor circuit. There are test procedures for both in the FSM but the fact that both codes appeared together could mean that the sensor is at fault. Code 64 is right O2 sensor indicating lean exhaust, which could be resulting from a IAT problem. Code 61 is not in my FSM, but the left O2 codes are 44 and 45. If you have access to a scanner you can test the IAT.

 

i can't find code 61 on any list either, so if anyone has any idea what that indicates, please chime in!

i do have access to a scanner at my buddy's shop so i'll test the sensor and see what happens. so at that point, assuming the sensor is the issue and is replaced, i guess i'll clear the existing codes and see if i get the O2 codes again. could a faulty IAT sensor cause the exhaust popping/backfiring/power loss i'm getting? i would think so right?

 

The IAT could indirectly cause those symptoms by sending erroneous info to the ECM which then makes incorrect adjustments to the air/fuel ratio. This could then cause the O2 sensor to report a lean mixture. It is also possible that the ECM is ailing, but, as usual, don't just throw parts at the problem.

 

the ecm is new (and was a major PITA to get) so i hope thats not the problem...
i'll definitely test the sensor before i put another one in but, worst case, they look pretty cheap to replace. $20 or so.

 

Good luck. Post back to tell us how you make out.

 

so i had my buddy at the shop run a test with his scanner on the IAT and it turns out it was in fact cooked. I pulled it, threw in another, cleared the codes and no SES lights since. I'm putting some highway miles on it this afternoon so we'll see if it trips anymore codes, but I would imagine that did the trick.

 

 

Inlet Air Temperature (IAT) went ****-up, huh? Good to hear the problem's solved. Another satisfied customer.