aaronk

My 94 22RE pickup has been running rough at idle since I bought it. When I say rough I don't mean that idle speed is jumping around but that the engine itself seems to be vibrating/shaking a lot (checked motor mounts and they are good). It will idle at a constant RPM but rarely at the same RPM. One stoplight it's a constant 750, another it's a constant 1000. The engine shaking/vibration smooths out when the RPM's get up to 1200-1400. When in gear and running everything sounds and feels fine. Another symptom, and I don't know if related or not, is the exhaust smells like it's running rich. If you're in the drive through behind me you'd better turn your air off There is no smoke coming from the exhaust, just a rich smell. However, I consistantly get 17-19mpg with 31" tires so the MPG seems about normal.

So, I'm trying to diagnose the engine shaking and decide to check the timing. I hook the timing light to the battery and the #1 spark plug and give it a shot. I'm not surprised to find that it's jumping around a lot, from about 12 to 5 on the timing mark. The previous owner had the timing chain replaced in 2006 and new plugs, wire, cap and rotor. I always go with OE on this type of stuff, but I don't think he did, the stuff that's on there seems pretty cheap. I'm not opposed to getting OE wires, cap, and rotor but I don't want to start throwing parts (and $$) at this problem.

Assuming I have no vacuum leaks, what would be your next guess as to why my timing is jumping all around? And second, do you think the engine shaking and rich exhaust is related to the timing problem?

Thanks!

notanymore

when your checking and setting the timing you have to jump 2 terminals.
http://www.4crawler.com/4x4/CheapTri...CheckConnector
that might help you out. and for the rich exhaust, i dont know for sure but couldnt if the timing was retarded too much it cause that? i dont know if it is or not, but just a thought

MMA_Alex

check the terminal thing. if it doesent drop then the tps is set wrong.

i'd also check for slop/play in the timing chain (pull the valve cover)

thook

The TPS being out of adjustment or just bad entirely is pretty common. So, go ahead and test that....(run "TPS" search).....it won't hurt. You'll just have to get an inexpensive digital multimeter. <<<Not a pointless investment.

amgraham

If the timing mark is jumping around under the light then it doesn't matter what the TPS is doing, that's slack in the chain. Pull the valve cover and check the chain and guides. If you have to replace it don't go OE.. Get the engnbldr or DOA metal guides.

tc

Whoa fellas - let's start simple:

Are the wires all fully snapped onto the plugs?

Cap/rotor OK? (If you don't know when they were replaced last, I would replace them - they DO wear out)

Is the gap right on the plugs?

When you clamp the lead on the #1 wire, is it separated from the others?

The DIAG jumper won't make the timing jump like you describe - it will just advance it.

justinking060310

Go watch your crank pulley rotate and make sure it is not wobbling - I recently had a balancer shred the key way and it made the timing jump around but still ran just fine- it finally threw all the belts and the bolt and pulley came off...

Reldnew

My 84 ran like this for years. Had a burnt valve, rough at idle but picked it up right around 1500rpm. I must have driven it 40,000 mi like this without any related issues.

aaronk

Thanks everyone for the suggestions! I'm slowly working through and checking all this stuff out. As I mentioned, it runs strong when not at idle, so I'm not super concerned about getting this figured out today, although the sooner the better. If I can't figure it out I might have to break down and take it to the shop...

n4ynu1010

Bad TPS made my 3.0 idle terrible but so did putting aftermarket plugs that had the wrong preset gap in them , and the varying idle problem I had as well was from not only the wrong plug gaps but also from a vacumn leak at the idle adj on the throttle body (worn out o-ring on the idle screw) did the same thing you are talking about with the wandering idle , I do not know if your Throttle Body Idle Adj is the same on your 4 cyl but it would be worth a check I guess .

Here is a link with your specs for checking TPS :

http://www.4crawler.com/4x4/CheapTri...PositionSensor

Also remember that your timing light is keyed by ignition pulses , so yes I would be looking at play in timing gears and or belts but I would also be making sure I do not have a bad wire (arcing to ground or to another plug wire), bad cap (arcing/tracing) , rotor , coil (arcing/tracing) or even a bad distributor that may have play and chewing on the pick-ups , lots of things could cause a irrattic timing mark when using a light and likewise the rough idle as well .

aaronk

Well, I did break down and take it to the shop.

Turns out it was a valve adjustment issue. They adjusted the valves to spec and the engine idles smooooth, albeit a bit low, and the exhaust is back to normal. I checked the timing, with the jumper this time, and it was holding at a steady 12 degrees. Take the jumper out and it advances off the alignment marks. So tomorrow I'll adjust the idle back to spec and retard the timing 7 degrees. Hopefully that will get rid of most of the pinging I'm getting right now.

Anyways, I didn't think valves out of adjustment could have caused engine shaking, timing jumping, and rich exhaust smells, but it seems to have been the root problem.

n4ynu1010

Wow , go figure , they must have really been out , great that you got it straight , the pain from the bill will fade slowly , My 4WD Jimmy SLS has to have motor mounts , not a backyard job , $200 for the mounts and $350 for the labor , ooooowwwwwwww , I used to work for GM Stealer and get the blasted mounts at a bit over cost , I cant believe all that for motor mounts and labor , in the old days you could do that with a jack in almost a hour , Down With Technology !!!! HeHe

naadomail

Shaking, and exhaust smell I can see. But timing jumps I have a hard time wrapping my mind around. Glad you got it worked out.

n4ynu1010

I can beleive all that from valves just can't beleive they could change that much to affect the motor all of a sudden or at all for that matter , go figure , but you got it straight so Happy Motoring and be nice to that motor .

n4ynu1010

I can beleive all that from valves just can't believe they could change that much to affect the motor all of a sudden or at all for that matter , go figure , but you got it straight so Happy Motoring and be nice to that motor .

thook

Here's a question for ya....

If the jumper advances the timing, the why does idle "drop"?

And another....

What do you mean seperated? As in, not contacting each other? Does it matter if they're in close proximity to each other?

tc

No, the jumper ensures you're at base timing (no advance) - so it should drop with the jumper.

It's an inductive pickup - if the shielding is not real good, it COULD be picking up the signal from an adjacent plug wire

Shoua

Also, the gas smell could just be an exhaust leak at the exhaust manifold, like mine.

thook

I knew what the jumper does, but you said it "advances it". I was just a little confused by your statement...that's all.

So, what does it mean if the plug wires are discolored/darkened in spots? The ones on my '92 are blue (NGK) and have these dark splotches....kinda like they're burned, but there's no melting. I'm wondering if that's damage to the jackets/shielding. Any know of this...seen it before? I've not tested them yet as that actually takes time....which I seem to have so little of these days. Except I seem to have time to be on the computer, don't I? (That just occured to me... )

tc

You need new wires. Most plug wires out there use a carbon core that cracks/degrades over time. The black/discolored spots are more likely coming from INSIDE the wire from arcing across those cracks in the center conductor - most all of the exterior insulation materials will withstand any heat they are likely to experience under the hood (unless you have an exhaust leak as mentioned above - and then it will be a long section, not spots here and there)

If you use carbon core wires, you have to be prepared to replace them every year or two (which is as long as the cap/rotor will likely last anyways)