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Rough Idle


ejin4499
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I've been fighing a rough idle problem since I replaced the engine. I recently read about using a vacuum gauge to diagnose different engine trouble. I put the gauge on there and it fluttered about 17 - 21 inches and when rpms increased the needle smoothed out. I looked around on the net and so far what most sites are saying is that is an indication of worn valve guides. I looked up what it takes to replace them in the FSM. I was wondering if anyone has had to replace the guides or if there is something else I should try first.

Also if I'm going to pull the heads off my beasty I'm going to do a total rebuild on them. Anyone seen a good guide on a simple port and polish job? what replacment valves should I look at. Would doing a three angle grind be doable in a home garage by a non machinist?

 

Thanks guys

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Update

spoke with a couple of local machinists they all said that they had never seen a vg33 head need new guides but that I might have a bent valve or something going on with my lifters. I don't get the classic lifter tick in this truck after the first 1 second on a cold start. Anyone have any feedback on bent valves or any other reason my valves wouldn't be seating proper?

Edited by ejin4499
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You should first and foremost be checking ALL of your vacuum lines... I had a rough idle and it turned out I actually MISSED one, the one for the fuel pressure regulator... That's kind of a big deal yeah.

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Hmmm...which vacuum line is for the fuel pressure regulator.....I've been fighting a crappy idle during warm up for a while but figure it's vacuum related....and I probably missed a line somewhere too....along with fixing the cracks in my air tube between the air filter and the throttle body.

 

thanks

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On the stock intake manifold/fuel rail it's on the very back of the intake manifold... It's hard to see, I had to get up on my radiator core support but you can also feel for it.

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Yes you are correct a vacuum leak would cause a rough idle. The reason I suspect its my valves (still trying to get a leak down tester) is because of how the vacuum gague was vibrating (http://www.secondchancegarage.com/public/186.cfm) Also I have replaced every hose on the top end of my engine and I have sprayed propane at every seem joint and fitting in the top and bottom end of the engine. If there was a leak the propane should have found it. BTW the wand from a household weed burner makes a great propane dilivery device. (http://www.harborfreight.com/propane-torch-91033.html) the bell unscrews and you have a wand with a bend in it and great control of how much propane at a time get released.

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Is it puffing oil smoke at start up? If so you need new valve guides. If not look elseware for your problems. Plus I've never, ever seen bad valve guides cause a rough idle.

 

And doing a 3 point vavle grind is doable if you've seen it done before. Even though you can do it with a dremel doesnt always mean you should. It would be best to take it someplace and have them charge you 2 bucks a valve to do it.

Edited by nismothunder
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So I did the leak-down test today and every cylinder was at about 10% pressure loss at about 90 psi. According to the gague that was pretty good.

 

All my spark plugs looked great no deposits and a little tan in color. (just realized I should have checked the gap while I had them out)

 

I rechecked all my hoses including the one on the fuel regulator nothing cracked or loose there.

 

I replaced the oil and the lope got a little better.

 

Sprayed some carb cleaner around looking for vacuum leaks no joy there.

 

I did however notice, after I stoped swearing at it, that there is a faint lifter tick on the driver side head. If one of my lifters wasn't pumping up all the way it wouldn't open that valve all the way, but wouldn't that spark plug be fouled and black if it wasn't able to push the exhaust out or bring in enough air?

Edited by ejin4499
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ok mine was a problem with a valve under the intake plenum called the idle control valve its been a couple of years so i cant quite remember but i found a fix that used intake cleaner sprayed into a vac hose until the engine stalled then i let it sit for a few min and restarted it but still had the prob so i tried it again and in 2 years its been perfect ever since i cant find the write up but will look at what hose i used on my pathy also it can be removed and replaced but u need to remove the upper intake plenum so thats why i cheeped out on a can of intake cleaner and like i said its been 2 years and perfect

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ok mine was a problem with a valve under the intake plenum called the idle control valve its been a couple of years so i cant quite remember but i found a fix that used intake cleaner sprayed into a vac hose until the engine stalled then i let it sit for a few min and restarted it but still had the prob so i tried it again and in 2 years its been perfect ever since i cant find the write up but will look at what hose i used on my pathy also it can be removed and replaced but u need to remove the upper intake plenum so thats why i cheeped out on a can of intake cleaner and like i said its been 2 years and perfect

I did unplug that harness to turn all that stuff off and see what happened but other than slow down to 500 rpm the loping stayed the same. I will probably tear the upper intake off and check/clean all the valves and hoses again. This will give me a chance to pull the valve cover and inspect the driver side lifters and cam.

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I removed the EGR and even without plugging the egr pipe connection the truck had way more power. I'm thinking I may have had a leak somewhere in that system. I had tested the EGR and bpt valve according to the fsm but ........

Waiting for the bolt to arrive to plug up the headers then I can give it a real test.

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Ok I think I'm narrowing it down a little. with the leak test I can rule out a head gasket, valve, worn rings or cracked block. I had a bad seal between my egr and intake manifold thats fixed now. I've blocked off the AIAC vavle. that leaves a few of the hoses under the manifold, the upper and lower manifolds, my idle control vavle my throttle plate houseing, the intake tube after the maf and carbon canister with all its hoses. Is there anything else that I missed as far as possible vacuum leak sites?

By the time I'm done hunting this down there wont be anything left under the hood.

:laugh:

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