2000 Tahoe - Idle Issues with A/C vibrations

[Jerome Nelson]

2000 LT 5.3L V8 2WD Tahoe, automatic running rough with A/C on.

Fixed:​

Items replaced/cleaned so far:
• Spark Plugs (new)
• Spark Plug Wires (new)
• Coils (all 8, new)
• Valve Cover Gaskets (it was fouling the spark plugs)
• Cleaned Throttle Body
• Cleaned Mass Air Flow Sensor
• Cleaned Air Filter (K&N)
• Techron Complete Fuel System Cleaner (x2)

NOTE: It has an electronic Idle, so I couldn't clean the Idle Air Control Valve (I don't think it has one).
It also doesn't seem like it has any vacuum leaks.

These items have made the Tahoe run 90% better - almost like new!!

Issues:​

However, these are the issues I'm still having:
A. Idles at 500 rpm, after warm-up. Is this ok? I've read it should be at least 700 or more.
B. When I turn on the A/C, the truck vibrates mildly. (This was MUCH worse before I did the fixes above)
C. I feel like it's lost some "get up and go". The engine still feels strong, but it doesn't like to accelerate aggressively (Like I just woke up an old man).

Questions:​

1. What is the appropriate idle speed? And, how do I adjust it, if 500 rpms are too low?
2. Is it normal for the truck to have a light shimmy with the A/C on?
3. Any suggestions on how to give it some more "umf" at acceleration?!

I appreciate any feedback/guidance you can give!

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot assist you much on your model year, but lots of folks here have NBS trucks, and they will chime in.

It is not normal for the truck to vibrate, when the A/C is switched on. Sounds like a compressor issue, but I would first check the A/C belt tensioner to ensure that it is not bad (worn out bearing).

 

[Doubeleive]

mileage?
your 2000 is drive by cable, not drive by wire so yes it does have a IAC and it can be removed and cleaned and you can clean inside where the IAC inserts.
the reason I ask mileage is because after about 160k the MAF can be really funky or flat out bad or erratic and cause all kinds of issue's, just something to consider.
500rpm is on the low side normally it should stay in between 500-600 after it is warmed up. cold idle maybe 1000-1100 or so for a minute or two depending on how cold it is.
other things that can help smooth out a idle is injector cleaning, running cleaner for a while will usually work but it takes more than just a bottle or 2 you have to keep at it

 

[Jerome Nelson]

It is not normal for the truck to vibrate, when the A/C is switched on. Sounds like a compressor issue, but I would first check the A/C belt tensioner to ensure that it is not bad (worn out bearing).

Thanks for the greeting, Joseph! I didn't think of the compressor or belt tensioner - that makes sense! I'll check this out.

 

[Jerome Nelson]

your 2000 is drive by cable, not drive by wire so yes it does have a IAC and it can be removed and cleaned and you can clean inside where the IAC inserts.

You are right that it should be drive by cable, and not by wire. However, I've looked over multiple photos and diagrams of what I should have, and what I do have, and it appears to be drive by wire. I'm not sure why, maybe the original owners got an upgrade! Attached is a photo of what I have. The IAC should be in that gap to the right. Also, notice that is a servo, not a pully. Weird.

 

[Jerome Nelson]

I just clocked 199,199 miles last night! I'll swing back by the MAF, but it looked pristine. I've had multiple mechanics say it looks like a 40,000 mile vehicle, so I can't complain!

If it's not overkill, I could run more Techron through it. I put some in about every 6-12 months or so.

Thanks for sharing!

 

[Sam Harris]

You said the valve cover gaskets were replaced, and they were causing fouling of the spark plugs. In my experience, the fouling of spark plugs is unlikely to be caused by a leaky valve cover gasket. I’d say the fouling issue needs to be further investigated. Do you have any codes..? Do you have an OBD2 scanner? Better yet, if you know anyone with a Tech2, this would be preferred.

 

[Jerome Nelson]

You said the valve cover gaskets were replaced, and they were causing fouling of the spark plugs. In my experience, the fouling of spark plugs is unlikely to be caused by a leaky valve cover gasket. I’d say the fouling issue needs to be further investigated. Do you have any codes..? Do you have an OBD2 scanner? Better yet, if you know anyone with a Tech2, this would be preferred.

Yes, I was wondering about the Spark Plugs being fouled by the leaky valve cover gasket. It just doesn't seem like it would leak that direction. I just don't know what else could have fouled them out though. (To be clear, they had oil around the treads, but nowhere else. Is this normal?)

I mostly just replaced all of the items above, as nothing had been replaced since I got it, and it's almost 200K miles.

Yes, I use the BlueDriver Bluetooth Pro OBDII Scan Tool. But, it hasn't shown ANY code for any of these things.

I actually didn't notice the misfire. (I thought it was just cracky from being old!) A tech at Advanced auto noticed it and suggested I do the maintenance above, which I did one at a time - just to see how each improved it. As I said, the Tahoe runs 90% better than it did! I just can't get rid of the vibration with the A/C on. (Still need to test the belt tensioner...)

 

[Sam Harris]

Yes, I was wondering about the Spark Plugs being fouled by the leaky valve cover gasket. It just doesn't seem like it would leak that direction. I just don't know what else could have fouled them out though. (To be clear, they had oil around the treads, but nowhere else. Is this normal?)

I mostly just replaced all of the items above, as nothing had been replaced since I got it, and it's almost 200K miles.

Yes, I use the BlueDriver Bluetooth Pro OBDII Scan Tool. But, it hasn't shown ANY code for any of these things.

I actually didn't notice the misfire. (I thought it was just cracky from being old!) A tech at Advanced auto noticed it and suggested I do the maintenance above, which I did one at a time - just to see how each improved it. As I said, the Tahoe runs 90% better than it did! I just can't get rid of the vibration with the A/C on. (Still need to test the belt tensioner...)

Yes, sounds like the fouled plug and misfire are co-dependent. If it was misfiring, it definitely should have thrown a code. I’d try hard to locate someone with a Tech2. Many of us have purchased our own knock-offs, which work identically to the GM OEM Tech2, but only cost about $300-350. I bought mine from “Chinacardiags”, and it’s served me very well. Well worth the small investment in my opinion. What part of the country are you in? Perhaps we have a member nearby, with a Tech2 clone, who could help.

 

[Doubeleive]

somethings not right, post up a picture of your rpo code list in the glove box that will explain some things
it's a sticker with a list of alpha numeric codes
does yours have a traction control button on the dash somewhere?
sounds like if the vehicle had the traction control option then it came with drive by wire
weird never seen one that early myself with dbw

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