Hello,

Curious if anyone/everyone notices a very slight shake only at hot idle.

I have a 98 S10 ZR2 (not a blazer, but this forum is great, so I joined), owned since new, currently at about 55k. Generally gets gentle use, but is usually carrying something - I dont drive hard/fast, but I carry a decent payload of stuff.

Anyway, when new, it seemed like at idle I couldnt even tell if the truck was on. For the last 25-30k, Ive been diagnosing (or trying to) this shaky idle. Ive done everything from caps/rotors to plugs and plug wires to heavier oils, etc.

The truck runs smooth and great, returns decent MPG and has good power. It is just the annoying idle shake, and it is only when hot. It is notable in drive and neutral, and with AC on and off. I can see the idle shake correlate with the oil pressure gauge fluctuating, but the RPMs stay steady at just over 500.

It feels almost like a misfire or leak through a spark plug wire. it is not severe, but noticable enough to feel it. I have never had a CEL, and Ive scanned it - always clean.

Any thoughts? Perhaps just the nature of the 4.3?

Thanks!

 

Try cleaning the throttle plate and Idle Air Controller with throttle plate cleaner. They tend to get dirty and cause a rough idle when the engine reaches normal operating temperature.

 

I have noticed the same type of thing on mine, what is the idle air controller? where is it?

 

Well, I did the IAC. I have an EGR gasket on order, but the results from the IAC is not promising.

Again, no codes, ever. I have a scangauge and scan with the engine on - nothing.

Here is what I did... pulled it out with a Torx 20 bit used:





The TB was quite clean though. Really not necessary to clean, even under the flap.



I cleaned it with CRC teflon safe throttle body cleaner.



I saw that the hole that the IAC valve sits in was pretty dirty black inside. I tried a variety of things to clean it, including spraying cleaner in there wiping paper and my fingers in the hole, and using a rag soaked in B12 chemtool.











And then put it back together...





I restarted it, and it took a bit of pedal, as would be expected, but then idled fine.

I let it idle a while, and noticed that it still shook. I looked at the scangauge, and wih the O2 in closed loop mode, water at temp, idling with AC and fan on to simulate a slight load, ignition was at 20 degrees at idle, 35 at 2500 rpm in neutral. I cant take it out tonight to get more data of ignition advance, not sure if it helps.

I then tried removing spark plug wires. I had my wife start the truck with a different one disconnected each time. It started perfectly, and there was a definite roughness due to misfire, but it was a very similar shake to what happens when it just shakes normally at idle. I have magnecor 8mm wires that are more or less new (within the year). Spark plugs were done less than 20k ago, to try to attack the idle shake (and did not help). I put the magnecor wires as an attempt to fix the shake too - no change comapred to OE wires.

Ive replaced the cap and rotor twice.

Ill attack the EGR within the week, after I get the gasket. Anyone think it will actually help?

Is a slight shake at idle jus the nature of a 60 degree V6? The engine mounts are solid, ive tried shaking them with no motion, which I should see if themounts were shot.

Any thoughts???

 

Very cool post by the way... No, General Motors did not make The 45 degree 4.3 V6 with a rough idle in mind. (or any other engine for that matter) Mine idles and runs very smoothly. Somethings up with it but you are gonna have to do some detective work to find it.
You are running AC Delco plugs right?

 

60*? 45*?... How about 90* v6... LOL

It sounds as though there is something else affecting your engine that is causing your idle quality problems.

BTW, nice pictures! If you want, you could make up a little how-to and post it in the Article Submission subsection of the Tech Article (DIY) section.