99 Ram Van 318

I have been reluctant to apply the correction for the leaking plenum gasket (causing knock and oil usage).

Now I have a code P1294 (Target Idle not reached) and a high idle.

Has anyone had the plenum gasket leak and if so, did it advance to a staqe that caused a vacuum leak getting air into the intake and causing the high idle?

In other words, has anyone else had a code P1294 that went away after a new plenum gasket?

I have checked the connections on the injectors, the sensors on the throttle body. Nothing on the motor has been touched in a while and it only sees very light duty, only driven to church on Sundays ;-)

Thank you,
Lee

 

A bad plenum could throw a ton of codes. The oil its burning could be getting caked on some sensors, or just building a ton of carbon up. I would get it replaced ASAP...it helps. I just did mine last week.

 

What makes you think the plenum is leaking?

Does your vehicle knock and consume excess oil?

 

Right, I've had the knocking and oil usage (no smoke, though and it passes emissions testing) -- started about two years ago.

I changed to a 180 degree thermostat, changed to a cooler (hotter / I forget) spark plug and started using premiuim gas (before the $3.00+ era).

That did help quite a bit, but I still have a occasional knock and about a quart per 1,000 miles usage. I could live with that, but the CEL and P1294 code and high idle are recent in the last week.

It's the wife's transportation so it needs to be tip-top!

Thanks
Lee

 

I have oil in the intake but when I performed the plenum TSB test, I had positive pressure buildup in the crankcase which indicates I don't have a leak. I don't want to tear it down if I don't have to. Anyone with a similar diagnosis?

 

What do you mean by positve pressure build up? It blew your thumbs off the tubes? Suction means leak.

 

It didn't blow my thumbs off but it had venting out of the breather tube when I sealed the pcv hose at the intake and the pcv at the valve cover.

 

So my guess is I don't have a plenum leak based on the test via the TSB. Has anyone had a similar outcome; pass the TSB but oil leak in the plenum?

 

Even if your plenum is sealed properly you can still have oily residue in the intake. Depending on your engine and PCV condition you might even have some slight oilpooling.
Best case it's gonna be grungy down there.

 

I had pressure like you are saying as it blew air out of the pcv and breather on the valve covers. I didn't have a lot of oil down my TB but had a tad bit starting to form at the rear. I had the pleneum fixxed anyway as I didn't want to mess with it in the future. I know my lower intake manifold gaskets had gone bad and I kind of think my pleneum had as well even though it didn't have suction when I did that test.