Diagnosing Rough Idle Hell

[Schurkey]

OOOOooooo..."notorious"!

I like it!

 

[DylChrFla]

Keep us updated. Im having the same exact issue you are having and cant seem to figure it out, with pretty much the same exact new parts and troubleshooting you did. About to order a ALDL cable to data log as Shurkey is notorious for advising people to do so lol.

Still am yet to figure it out, I can’t locate or hear a source of vacuum leak but I’m starting to think vacuum might be causing my issues. I’m going to replace my lines and see if that helps.

 

[tsr2185]

Still am yet to figure it out, I can’t locate or hear a source of vacuum leak but I’m starting to think vacuum might be causing my issues. I’m going to replace my lines and see if that helps.

Gotcha. I replaced all my lines and still same issue. Im offshore right now and I just learned about the booster check valve and vac line going to it (im till a noob). I used a butane torch to check for leaks but I didnt find any either. Didnt use starter fluid, but will try that when i get home, along with the datalogging and TBI rebuild.

You did a compression test, fuel pressure test, and put a vac guage on it? I havent put a vac guage on mine, but the other two check out fine.

Let us know. Ive searched dozens of posts about rough idles, and 90% of the time the O.P. never follows up with their solutions lol.

 

[DerekTheGreat]

Yeah, a compression test would be a good thing. WHen you pulled the plugs that were in it, how'd they look? Any idea how long were they in there? You say you've got aftermarket headers on it but stock O2. I've heard that aftermarket stuff doesn't play well with the stock O2 as it will no longer get hot enough and then sends weirdness to the computer which results in drivability concerns.

 

[DylChrFla]

Yeah, a compression test would be a good thing. WHen you pulled the plugs that were in it, how'd they look? Any idea how long were they in there? You say you've got aftermarket headers on it but stock O2. I've heard that aftermarket stuff doesn't play well with the stock O2 as it will no longer get hot enough and then sends weirdness to the computer which results in drivability concerns.

I haven’t performed a compression test but that would be a good one to know. All of the plugs had identical regular wear with no signs of running rich. They read possibly slightly lean. Honestly they were in good shape but I changed them anyway. Maybe had 15,000 miles on them. I’m not sure if O2 has anything to do with my problems, as the data logging read normal and I still had the same symptoms with the O2 unplugged and in open loop. I also think I had these symptoms before installing the headers.

 

[DylChrFla]

Gotcha. I replaced all my lines and still same issue. Im offshore right now and I just learned about the booster check valve and vac line going to it (im till a noob). I used a butane torch to check for leaks but I didnt find any either. Didnt use starter fluid, but will try that when i get home, along with the datalogging and TBI rebuild.

You did a compression test, fuel pressure test, and put a vac guage on it? I havent put a vac guage on mine, but the other two check out fine.

Let us know. Ive searched dozens of posts about rough idles, and 90% of the time the O.P. never follows up with their solutions lol.

I’ll keep you posted.

 

[DylChrFla]

Still haven’t found the issue but I tried unplugging the O2 again and noticed it does idle much better while in open loop. Still noticed the roughness every once in a while but I‘m thinking it has to be O2/fuel related.

 

[DylChrFla]

I did run a vacuum gauge after replacing all my lines, had a reading of 21 in Hg with no change even when rough idle was occurring. I also noticed in my datalogging that my idle is a bit high, it tends to hover around 825-875 rpm.

 

[Schurkey]

Does the IAC work properly? Can you tell what is commanded idle speed vs. actual idle speed?

 

[DylChrFla]

Does the IAC work properly? Can you tell what is commanded idle speed vs. actual idle speed?

I'm not familiar with the term commanded idle speed. Is that what is set by the screw with the IAC unplugged?