98 Blazer Missing/Shaking when idling

[chevygirltse]

I have a 1998 Chevy Blazer LT. I have fixed absolutely everything I can think of. I replaced a camshaft position sensor in January, because the SES light came on and the code said that's what it was. Ever since then, when it is idling, the car shakes/idles rough and it feels like it might stall. It has gotten progressively worse in the past two months. I don't think it's missing(would the SES light not come on to indicate misfire?), and we have replaced the fuel filter, air filter, oil changed, plugs, wires, distributor cap and button, and vaccuum hoses. It is passing Diagnostic Tests when taking it to a garage. I know something is wrong, but the technician said nothing is showing up. Is there anyone who might know what this could be? Thanks for any suggestions!

[Blue Bowtie]

Welcome Aboard!

Has a cylinder leakage test or cranking compression test been performed? Either of those might help identify mechanical damage, such as poorly seating valves.

Do you have a vacuum reading at idle? Is vacuum steady, or bouncing cyclically?

[MT-2500]

Does it miss or run good on the road?
What was the code no on camshaft sensor?
Are you getting any check engine lights blinking or a steady light?
What brand or kind of plugs did you use.
MT

[Weezow1]

My 1995 4x4 blazer had the same problem. This may be my fist post on AF, but iv'e done a lot of research on my problem. Turns out it was the EGR valve. Make sure you have checked that. If it is loaded with carbon, the valve could be getting stuck open or closed, causing rough idle or stalling. You should be able to clean it out with carbeurator cleaner as long as you dont fill the thing up with it upside down (thats how i destroyed mine)

Also, when I had my bad EGR valve, it did not generate any code nor did the engine light come on.

[chevygirltse]

Thanks to all who replied. I got mad and tired of messing with it, so I took it to yet another garage, and it ended up being the idle control motor and the thermostat(???). Did not see that one at all!!! Will still check out the EGR valve though. Thanks again for all the advice!

[chevygirltse]

Okay, I have another question about the 98 Blazer. If my water pump was going out, could the afore mentioned symptoms be part of that? I brought the stinking thing home from the garage yesterday, and i went out to the garage tonight to work on that EGR valve, and noticed a huge puddle under the Blazer. So one of my friends, who knows more than I do about cars, said my water pump went out. Would that have had anything to do with the engine trying to stall or missing/shaking when idling? I am not sure that the two could be related, but if anyone has an opinion or theory, I would like to hear it!

[muddog321]

If a thermostat was replaced did they flush the entire cooling system or just top off the Dex cool after it? Most Blazers start a lower intake gasket leak by 100k miles so look closely for that leak - is it in fact coming from one of the two WP holes or is it from the mating between the block and intake - a good light should be used. Then also look along the sides between the valve covers and intake and then feel the rear for leaks. Common is after a system flush or intake the Dex cool sludges up and takes the WP out (and heater core). Welcome to the GM 4.3 Blazer!