[Mgilla]

Ok, peeps, I've read about everything I could get my beady eyes on - but really haven't come across a similar situation. This '01 was acquired through an Ebay auction as a parts car for my damaged '99 STS; however, I was forced to put it into service until such time as I can make the changeover. Initially, the car ran fine, with just a slight miss; but over several months, the idle roughness and bad gas mileage and engine surge/odd shift points made me park it and acquire a '00 El Dorado driver. That car is now a boat anchor because of a head gasket/overheating issue (if anyone were interested).

PCM codes I pulled on the '01 STS were P0101, P0171, & P0174 - typical vacuum leak indicators. So, I replaced the intake gaskets and throttle-body rubber coupler. After clearing the codes, I restarted it and reread the codes. P0171 and P0174 disappeared, but P0101 was still current. So, I took off the MAF and discovered a small amount of leaf debris on the screen - cleaned that; found a loose TB coupler bolt - tightened that; made sure everything was buttoned & fixed tightly, then reassembled it all. All codes are now gone. BUT - I am still experiencing rough idle, engine surge, and even though I haven't yet driven it, feel it will probably have the odd shifting issue again.

I have yet to clean the TB bore or IAC. I read where a stuck EGR could cause drivability issues, as well. Any ideas?

Wayne--

 

[Submariner409]

Clean the TB, IAC, and EGR pintle and seat.

Your 2001 and 2000 powertrains (engine and electrical/electronic/transmission controls) are VERY different from the 1999 ..................and you need to match VIN 9 to VIN 9 - and VIN Y to VIN Y.

 

[Ranger]

:yeah: Clean the TB.

 

[Mgilla]

Thanks, Ranger - will do.

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Thanks for the quick response. This '01 STS is just a parts car for my '99 STS front clip and radiator/support structure (a 14-year-old with a learner's permit backed up four feet and totaled it). Everything else was going to be a parts car to keep the '99 alive for many more years, but I really don't want to start my own salvage yard - so I'll probably part it out on eBay or craigslist. The '00 El Dorado is in fairly good shape, considering the engine just bit the dust; I'll try and just sell it outright as a parts car.

I placed a couple of pics of my '99 on the show me your ride sticky.

Wayne--

 

[Mgilla]

Ok, guys, I put in a new air filter, replaced all the plugs, cleaned the TB, iac valve, and the egr valve (which wasn't sticking at all). The only thing I haven't done anything to is the TPS; why would anyone use Phillips head screws to bolt an engine component on? After buttoning everything back together, it still runs rough with fluctuating rpms. As I noted earler, before I did anything, it was throwing P0101, P0171 & P0174 codes. After cleaning and replacing stuff, it isn't throwing any codes at all (it does throw one code, but that is an ABS code - I noticed the wires are off the brake pads, but I'm not sure that by itself would throw an ABS code).

I'm somewhat at a standstill here; with no codes being displayed, diagnosing a computer-controlled engine that appears to be misfiring and experiencing rpm fluctuation is becoming a problem for me. I may just have to bite the bullet and take it to someone with more sophisticated diagnostics equipment.

 

[Submariner409]

Did you use the correct AC Delco #41-987 Platinum plugs, and check the boots for carbon tracking ? Also, the ICM in the L-leg of each coil cassette is removable - there's another multi-pin connector, with seal, in there. Sometimes - sometimes - condensation or moisture from engine washing causes shorts there = engine miss.

Click my username, open the profile. Left column - 2 albums 6 pages of pictures and diagrams for a post-2000 Northstar car.

 

[Mgilla]

Well, sir, I didn't use AC Delco plugs - I used Bosch platinum plugs, which is what the parts guy showed me were the factory-recommended equivalent, I guess. The boots were surprisingly new looking. Funny you should mention condensation in the ICM; the engine was running fine after the plenum coupler and intake gasket replacement, with just a slight miss, until I washed the car - then it seemed to just get worse. I didn't know the ICMs were removable; do they have a history of malfunctioning, and are they replaceable?

 

[Submariner409]

Northstars do NOT like Bosch spark plugs. They are not the Forum or GM recommended plug. Use the 41-987.

Sometimes the inside of the plug boot - area that slips over the plug ceramic insulator - develops carbon tracking. That completely or partially shorts out the high voltage path and causes slight or radical missing. Just one more area to check.

Both ICMs are identical and replaceable. Any junkyard or www.car-part.com .

 

[Mgilla]

Really?! There's that much difference between the brands that it would make such a difference? Compared to the plugs I pulled out (which, by the way, were AC-Delcos - and I'm thinking were the originals) you'd think new plugs would have made a drastic difference, regardless of brand. I, seriously, do not relish the idea of replacing those back plugs - ever; that was such an ordeal. I believe I'll go out to the shop and take a peek at the ICMs; I'll get back to you later. Thanks for the quick replies - it really is appreciated when someone takes the time to help out a complete stranger.

Wayne--

 

[DsharK]

it really is appreciated when someone takes the time to help out a complete stranger.

So True!

 

[Ranger]

Have you verified no vacuum leak at the PCV line in the rear cam cover?

 

[Mgilla]

Well, not really; I do know that it's snug-fitting because the first time I put the intake manifold back on, that line came off of the nipple inside. I had to take the manifold (and fuelrail) off again to reinsert the line. Odd that the nipple wouldn't be barbed. A local mechanic my brother knows proposed that I unplug the MAF sensor and see if the engine runs smoother - if it does, he'd replace the MAF sensor. I didn't think the engine would even run without the MAF sensor installed; but he said it should go into a default mode and run. I'll give it a try, but I'm also skeptical. I have to head off to work now, so I'll pop back in later today. Thanks again!

 

[Ranger]

A local mechanic my brother knows proposed that I unplug the MAF sensor and see if the engine runs smoother - if it does, he'd replace the MAF sensor.

I agree, especially based on your previous P0101 code.

 

[Mgilla]

Well, peeps, after a few days of rainy, dreary days, I fired up the '01; it immediately jumped to 1100rpm, for about 25 seconds, with a definite miss, whereupon it dropped to about 1000rpms, and started chugging really bad. After 10 seconds of that, I shut it off and read the codes. The ABS was still there, with no other codes thrown - except a P0300, which is what I would have expected before this when the rpms dropped to a chugging 900rpms. Anyway, I pulled the MAF sensor harness and started it back up. It immediated jumped to 1100rpm - but it ran smooth! I let it run for about two or three minutes, then shut it down and read the codes; other than that ABS code, only the expected MAF P0102 code was current. It would appear that I may consider taking a trip to the parts store for a new MAF sensor, eh!?

 

[Submariner409]

Factor into your idle problems that, cold, the engine is supposed to start and run at about 1200 rpm for some seconds, then drop to 900 rpm or so for a while, then to normal idle of about 650. Idle speed change timing depends on ambient temperature and coolant temperature.

The electronic equivalent of the old carburetor/heated choke "fast idle cam".

 

[Mgilla]

I concur with the fast idle speed on a cold start, but to act like it was going to die at 900-1000rpm was somewhat disconcerting - which is why I didn't let it go for too long. The surprising thing, though, was it running smoothly without the MAF sensor, albeit faster than usual on a cold start (it went from 1100 to 900, then back up to 1300). After two or three minutes of running around 1300rpm, it started to warm up - to about 160 degrees before I shut if off, but it didn't seem as though it was going to drop to idle speed any time soon.

I've looked around for a MAF sensor, with the least expensive Cardone brand around $80; Delphi goes for $128; Dorman at $165. The wallet speaks.

 

[Mgilla]

UPDATE: I put in a new MAF sensor and it sorta didn't run right. It runs better than the old one, but there's still that unmistakable miss. I did this about five times, where I started it, ran it for a few minutes, shut it off and then read the codes. No codes. Well, on the last run, I let it warm up some to where it began dropping the idle down to around 700rpm, but it still feels like it's not firing on one or more cylinders. When I goosed the gas a bit, ranging from 1,500 to 2,500, it wouldn't hold a steady rpm - it sorta fluctuated up and down about 500rpm. On that last run, it threw a DDM B1621 code. I cannot find any reference to that particular code anywhere. The DDM, I find, stands for Door Driver Module, but the B1621 is nowhere associated with DDM - I'm not even seeing a B1621.

 

[Ranger]

Whatever it is, it is a Body code and unrelated.

 

[Mgilla]

I'm going to attempt to drive it a few miles today and see how it behaves. The fluctuating rpm issue, though, is one that occurred before I replaced the MAF, so I'm not sure that issue will go away yet. I'm confused by the roughness the engine is exhibiting, yet there are no codes being thrown that would point to a specific problem. I've built some strong, carburated engines in my time and in those instances where a rough idle, and/or fluctuating rpm arose, there were logical approaches to determining the issue. However, I'm not quite as good at diagnostics with these computer-controlled engines. It used to be simple: spark, air, fuel. About a year ago, I rebuilt my brother's Boss Hoss 350 V8, down to replacing even the cam bearings. He now has a near-500hp, carburated motorcycle that is simple to tune. Maybe I should just replace the Northstar with a carburated motor!?

Well, I just took it out for a spin of about 10 miles or so. It seem to drive fine; it even kept cruise control settings. However, when I disengaged cruise, there wasn't any immediate slow-down - the engine was pulling on its own, enough to keep it rolling along with no gas input at 40mph. When I got back, I placed it into neutral and it was idling at 1800rpm - and it threw a P0101 code, to boot.