Hey Guys,

I'm a casual lurker of the forum and found it super useful for some fixes on my truck, I'm hoping you can all point me in the right direction.

I've got a 2001 jimmy slt, I bought it about 5 months ago from a guy who basically had it sitting in his farm for 8 years (would casually ride it every month or so for hauling stuff around). I bought it with leaking gas lines and fixed it up. Also changed out the brake pads and rotors, fresh oil change, etc. Check engine light came on a few weeks later with P0446. The gas gauge is also broken so i thought the two were related (i planned on putting in a new tank, sending unit, etc).

Now: I've been getting a rough idle and decided to check the codes. The same P0446 was there, as was P0306, the cylinder 6 misfire, P0410 (secondary air injection system), and P0117 (engine coolant temperature sensor). I changed out the plugs on all 6 cylinders, cleaned out the airbox (it was a mess with dead leaves and twigs) and replaced the air filter. I still had the rough idle. Interestingly, it only idles roughly; when i give it gas it runs fairly smoothly.

From here i decided to check my vacuum lines. I found a line disconnected from the charcoal filter in the engine bay on the driver side fender. I attached it, drove it, and while still giving me a bit of a rough idle it hasnt shown codes P0446, P0117, and P410 since.

From here I ran a fuel system cleaner with a full tank of gas, and while not as rough, its still giving me some vibration at idle. Now, it would start and idle well, but then give me some vibration after a minute or two. I ran the codes again and got the same P0306 (as expected) and then a P0101, the mass air flow performance problem. I cleaned out the MAF sensor with some MAF cleaner and reinstalled. Same thing; starts well, idles well, drives well, but gives me a rough idle as i keep driving. Now the check engine light flashes intermittently and im getting a bit of clear white smoke under the driver side door sporadically. It smells a little sweet and this has me concerned enough to park it for the time being.

Well guys: where do i go from here?

 

Sounds like a possible lower intake manifold gasket leak. Beg/borrow/steal a cooling system pressure tester and check it for leaks. Pay special attention to the #6 intake port area.

 

Good suggestion.

At some point you may need to check compression.

Did any of the plugs look funky?

Have you looked at the wires, distr cap and rotor? Try swapping two wires with #6 and see if the problem follows. Also get a spray water bottle and look for arching in the dark.

What does the oil look like?

You should rule out more vacuum leaks and air leaks in the intake after the MAF. Turn the truck off, unplug the MAF restart. How does it run?

What happened with that ECT, a bad signal can cause the truck to run lousy?