I love my 97 blazer but for years its had a rough idle, it idles at about 550 but will dip and shudder and then return doesn't matter how long it's been running it had an engine swap about 40k miles ago and since we've changed plugs and wires a few times, the maf sensor, egr valve, fuel filters, distributor dizzy cap and rotor, throttle position sensor, idle air controller, also cleaned the throttle body. I also recently changed the radiator cause my dexcool turned to mud flushed the whole system no change. I was thinking maybe the intake manifold gasket because of the dexcool does that sound reasonable?

 

I hope you find out because my idle is erratic and it creeps me out. Regarding the coolant idea, I don't think so. If there was a rip in the gasket between the coolant port and the port into the cylinder, coolant would be getting sucked in and you would see white steam in the exhaust.

 

Im thinking pcv valve now as that's the only thing Ive seen on here that I havnt tried

 

I had an 02 ford once with a bad idle. Smoke test revealed a seriously large rip in the PCV hose, I fixed it and that fixed the idle. The part cost $8.00, the smoke test cost $80..


though, https://blazerforum.com/forum/articl...e-tools-79674/

 

The pvc grommet was pretty worn so I'm going to replace that along with the pic valve

 

PCV valve is one of those items that should be AC Delco, not a store brand. Try to check the hose for cracks. The original post symptoms sound like the classic IAC gone bad. But you replaced that. Take another look at that to be sure that the harness and connector are both good, gasket is good and so on.

 

I'll check it out once the car is back home. If I remember right it is relatively cheap so I might just order a new one.

 

Idle on my 4.3 improves when I put it in neutral. Wonder if changing the transmission oil would help? Or, is there a vacuum hose that goes to the transmission?
Puttster

 

puttster: have had this problem for over two years and really doubt that changing trans fluid will help any....however if the fluid has not been changed in 75k miles....would not hurt to do so. Be sure to do the filter as well.

Be prepared for a very messy job. On some years the exhaust cross-over piping interferes with lowering of the trans pan straight down; such that the pan has to be tilted towards the rear and then towards the front causing fluid to spils over the edge. Use a large catch pan and have a sack of kitty litter at the ready.

 

Turns out my brake booster had a pretty bad leak got it changed idle is a lot less rough but not perfect and the brakes are great now but now the service engine light came on so as soon as I get it home I will check the code