[EcSTSatic]

I have this irregular shake at idle. It's not a constant 'miss', it's random but frequent and it happens whenever I'm stopped or in Neutral. Goes away if you give it any throttle at all. The ACDelco plugs have about 50K miles. The wires are original at 127K. The FPR isn't leaking and it has been replaced a couple times for hard starting. No codes. Don't see any vacuum leaks. Could it be bad gas or maybe the wires? It disappears completely anywhere off of idle. I hate to throw parts at it. I put some Seafoam in the tank while I try to figure it out. Any suggestions are welcome.

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Forgot to mention both crankshaft position sensors were replaced about a year ago for a stalling problem. I'm going to order new wires because they are overdue. This problem came on sudden like. I thought it might be all the rain we are getting but the engine compartment should be dry by now.

 

[Submariner409]

SWAG (Scientific Wild Ass Guess) - but the plug wires are well overdue (time and mileage) for replacement, as is a thorough coil and ICM removal and cleaning. Here's your plug-to-coil arrangement. The proper order is important - Google "waste spark ignition system" for insight.

 

[Ranger]

Putting solvent in your tank won't help anything, but with 127K on the wires, they have to be suspect, especially if they have recently been moved around for any reason.

 

[EcSTSatic]

Thanks guys. Wires are on order. I'll service the other components in the system. I've read where coil terminals get rusty, but mine are all clean. Nice diagram.

 

[basscatt]

Thanks guys. Wires are on order. I'll service the other components in the system. I've read where coil terminals get rusty, but mine are all clean. Nice diagram.

=====================
don't forget to clean the throttle body and IAC solenoid -

 

[EcSTSatic]

I'm spoiled by Amazon Prime. I would be getting my wires tomorrow. This order hasn't even shipped yet. I'll be cleaning parts until then. Still have the backup switch problem to figure out too.

 

[EcSTSatic]

Installed my new wires tonight. Still have the same problem. The "Service Engine Soon" light came on earlier today. Still no codes. I have a hard time thinking my plugs with on 50k miles are bad. I may try an FPR tomorrow and check my fuel pressure.

 

[basscatt]

Installed my new wires tonight. Still have the same problem. The "Service Engine Soon" light came on earlier today. Still no codes. I have a hard time thinking my plugs with on 50k miles are bad. I may try an FPR tomorrow and check my fuel pressure.

========================
The "Service Engine Soon" light came on earlier today. Still no codes.
just can't be -

when the SES light is illuminated -
it is a result of an emissions problem - and a code must be set -

the code MIGHT go to "history" by the time you check for codes -
but there must be a "P" code stored -

 

[EcSTSatic]

You're right. There was a code in History. I cleared them to see if it comes back. No engine light this morning. FPR going in today. The roughness is getting worse. Hesitation on acceleration.

 

[Ranger]

Did you check to see if the FPR was leaking? It takes about 15 seconds. Arbitrarily changing it may be a waste of time & money.

 

[EcSTSatic]

Did you check to see if the FPR was leaking? It takes about 15 seconds. Arbitrarily changing it may be a waste of time & money.

I did. It was one of the first things (easiest) to do. I already arbitrarily changed the wires. Still don't think it's plugs, so I will gamble on a $50 FPR.

Well. I'll stay away from Vegas. FPR didn't help. Maybe it's an injector. Low end acceleration is getting sluggish

Found a test sheet on Autozone to measure the primary and secondary windings of the coil packs.
http://econtent.autozone.com:24999/znetcs/psb/en_US/2/0/27/c849_coil_specs.pdf

 

[EcSTSatic]

FIXED! It was the 3-8 coil. The secondary winding was open. I was riding on 6 cylinders today!

 

[Ranger]

It's always the last thing you check. Glad you finally nailed it though.

 

[EcSTSatic]

Thanks. Hopefully this thread adds to the knowledge base and helps someone else like other threads helped me.