Fixing the idle and high BLM

[UncleDave]

I'm having a bit of a chore figuring out the cause of a rough idle, and slight miss at part throttle with no load.

The ScanMaster is reporting the following at idle:
MAF: between 4 and 5
O2: moves a lot between 00 and 700's, but usually around 500's to 700's
TPS: .44
IAC: between 10 and 20, higher when warm, but has been 00 at times
INT: 128
BLM: 134-137
Don't recall the LV8 (low) or cc numbers.

The BLM, while higher than I'd like, seems to be within the acceptable range. RPM at idle is aorund 800. It just idles rough and the exhaust smells a little rich. Off-idle throttle response is good, no stumbling.

At light throttle and light load, up to approximately 2000 rpm, it seems to be missing, also when coasting it misses and the O2 skips around between almost 00 to 700 or so. Seems to run fine under load, and at WOT it pulls well with never any more than a 0.2 KR, usually 0 KR at 17-18psi.

I don't have a vacuum gauge, but I'm considering swapping my boost gauge for a vacuum/boost gauge. I checked for vacuum leaks using carb cleaner, but was unable to detect any. Also made sure all hoses between turbo, intercooler, up-pipe and TB are tight.

I'm using a good coil pack and module, R43TS plugs gapped to a tight .035, new AC Delco 8mm wires. As I mentioned the missing is not under load or WOT, just under no load or light load at lower rpm's.

So what else could cause the rough idle and low speed miss? Malfunctioning PCV, compromised intake gasket, possibly an exhaust leak?

Thanks,
~Dave

 

[UncleDave]

No responses... So, this is normal?

Forgot to mention: new fuel filter, oil looks good, not using oil or losing coolant, new fuel pump, pressure set to 43psi line off. No MAL codes set. Only other anomaly is the blue puff at startup (possibly valve seals). Coolant temp setting on ScanMaster appears to concur with the gauge.

?

 

[usetaboost]

Your iac count should be around 10-20 when fully warm. Make sure it is. I myself like upper teens so it's got some wiggle room. It could very well be an exhaust leak on your elbow. Turbonut85 fought with that bastard for quite some time. Also check your egr to make sure it is sealing good. Whatever leak you have is small. Check and make sure your pcv valve is clean. Hose the crap out of it with brake clean and blow a little air through it. Check any small plastic lines or the phony ass way the vac lines are mounted with the 25 yr old plastic junk. If all else fails and you still haven't found a leak, pull a big vac hose off and stick it in some tranny fluid for a bit and it will smoke out of wherever it goes.

ALso, run a denso 02. They're cheap

 

[UncleDave]

Thanks Usetaboost. I will check all of the above. I've been contemplating getting rid of the stock hard vacuum lines also, just haven't decided which method I want to use.

Thx
Dave

 

[UncleDave]

Tightened up the DP - to - turbo, and had to tighten a couple header bolts also. BLM still at 134.

I'll try the trans fluid trick when nobody's around... Last time we did that, it was a practical joke on my Bro after his wedding reception. He was blowing so much smoke he thought he blew a head gasket! He laughs now, but at the time he wasn't too pleased. :tongue:

 

[Dabigguy]

Do a compression check, could be a blown head gasket.

 

[TurboBuRick]

Tightened up the DP - to - turbo, and had to tighten a couple header bolts also. BLM still at 134.

I'll try the trans fluid trick when nobody's around... Last time we did that, it was a practical joke on my Bro after his wedding reception. He was blowing so much smoke he thought he blew a head gasket! He laughs now, but at the time he wasn't too pleased. :tongue:

BLM 134 is not that bad at all.

I'm assuming that TT chip has open loop idle? What is the o2 millivolts when idling?

 

[UncleDave]

Do a compression check, could be a blown head gasket.

Compression is fine, but that was a good suggestion, thanks.

BLM 134 is not that bad at all.

I'm assuming that TT chip has open loop idle? What is the o2 millivolts when idling?

O2 is erratic but seems to show between high 400's up to 700's, it moves around a lot. I understood this was normal under closed loop, what about open loop?

Actually, yesterday it seemed to run fairly well, or else I'm just getting used to it... Some days it seems more "off" than others.

 

[Bigjack7440]

My o2s have always been 63/354/687/808 until I make a WOT pass then there 777@ 22-25lbs of boost and the BL# are always 122-124@ idle and 118 going 55@ under a WOT pass.

 

[Clark6]

Also at idle check to see if your 02's touch the 800s at all.
You showed 700 exactly 7__? Let it idle about 10minutes to make sure its warm then watch and see how the 02 #s scroll up and down write down or remember the highest number and the lowest number, to see if it climbs into the 800's at all even if it's once.

Do the same while driving around. You should get above 800 somewhere down the line while driving. I had one 02 sensor that wouldn't go above 730 but cycled the low numbers and below that fine.

put a new denso in then it went up to the 800s.
This shouldn't have anything to do with the rough idle issues that you have as you already have some good suggestions with that. My bls are around 137 after warmed up (idle) but driving around its back to 128 then back at idle back to 137-140. and vice/versa. I just noticed the o2 sensor may not be cycling hi enough on yours and thought i'd share input.

 

[UncleDave]

The car is getting trans work done but will check the O2's again as soon as I can. I don't ever recall it hitting the 8's at idle, but it definitely has when cruising. It's an AC sensor, I have a Denso sitting on the bench.

And, I'm still not convinced all my vacuum leaks are gone...