Shaky idle

[Pertti K]

A bit same issues as in thread chasing my tail in a poor running motor. help., but I decided to start a new topic to prevent two cases from mixing up.

Background: bone stock Typhoon, 114 kml on the odo. Has been a daily driver for the past 7-8 kml and 10 months. Before that it sat for 5 years. Mostly it has been working ok.

I've had issues with the ignition before and this is what I've done so far:
1. Replaced the spark plugs. Helped a lot. I guess I blew them when I had a major leak in the vacuum hoses.
2. Replaced the distributor cap and rotor. Again helped a lot, but then got worse after a while.
3. Replaced the spark plug wires, coil and vacuum hoses. Helped a bit.

After all it still has a uneven idle and vibration when revving on neutral. First it had the vibration up to 2000 rpm, but now it seems to continue on higher revs as well. Once when I stopped for gas and then drove 3-4 miles it had a smooth idle but when I shut it down and started up again the issue came back and has been there since.

Yesterday I did some checking:
- Changed the plugs once again (NGK UR5 0,035 gap)
- Checked the wires and sprayed them whit water to see if there were any sparks
- Took one wire at a time off and checked if the idle got worse and it did
- Visual check for vacuum leaks
- Ignition timing check
- Checked the ground points at the back and front of the LH cylinder head (3 pieces - are there others?)
- Compression test, all six in 140-150 psi range.

No help. You can feel the shakiness also at steady cruising speed, at least sometimes. With half a throttle or more it always runs great.

Any ideas how to proceed? This is what I have in mind:

1. Sometimes while cranking the speedometer needle jumps to 50 mls. Ignition key? Could this have something to do with the driveability problems?
2. Need to get a cable and learn to use the Datamaster.
3. Could be a converter issue (the vibration, not the uneven idle), but I doubt it. It doesn't get worse at higher rpm (earlier it got better in fact). Once the problem was off totally. And when revving the vibration almost disappears when I take my foot off the gas, and then comes back again on idle.
4. Vacuum leak check with start pilot or such
5. Ignition module. Is there any way tho check it? Or just go and replace it?

What else? Thanks a lot for reading.

 

[Davemc1963]

Re: Shaky idle

Any check lights , or fault codes stored?
One issue I had once that caused issues, was one of the plug wires wasn't properly 'clicked' onto a plug. I was convinced all was well. Pretty much a schoolboy error, but caught me out. Obviously when you say you have checked the wires, I presume that you have checked the resistance of each while flexing them to make sure there are no internal issues.
Another time after routing around the distributor and HT wires, I inadvertantly kinked the vac hose from the rear plenum fitting to the MAP sensor. That caught me out as it is a little hidden.
You could check/recheck the connections to the map and other connections like the coil and ignition module. I believe the small coil sub harness sometimes goes hard and brittle. (Mine seems ok, but still worth a look).
You could try running with vac hose to the egr disconnected and plugged (if you have one fitted).
Have you checked fuel pressure?
Other than that, you could try running supplemental grounds to see if that helps any.

 

[Pertti K]

Re: Shaky idle

Good comments, thanks Davemc1963.

No fault codes.

I've checked that the wires are properly installed several times. But wouldn't hurt to check once more. And no, I haven't checked the resistance, after all they're brand new, but you never know. They were one of the cheapest sets at Rockauto I thought of buying another set and changing them one by one.

Sorry, I didn't understand what you meant by "small coil sub harness".

And no, I haven't checked the fuel pressure either, haven't got a proper gauge.

One more thing I had in mind: the oxygen sensor. Can you check it just by unplugging it for a while?

 

[HAMMERHEAD]

Re: Shaky idle

I had a vibration issue years ago with my GMC Sierra pickup. It idled smooth, but when I would rev the engine, it had a bad vibration. Felt like a plug wire was off and was running on seven cylinders. It ended up being a bad torque converter.

 

[gringo76]

Re: Shaky idle

I had a vibration issue years ago with my GMC Sierra pickup. It idled smooth, but when I would rev the engine, it had a bad vibration. Felt like a plug wire was off and was running on seven cylinders. It ended up being a bad torque converter.

you mean 5 cylinders, they usually loose one not gain one. jk

 

[Pertti K]

Re: Shaky idle

Probably a V8 Sierra. Is it possible to unbolt the converter and then rev the engine or will I end up breaking something? But judging by the symptoms, I'm pretty convinced it's not the converter. Or at least there's something else as well.

 

[Syclone #1188]

Re: Shaky idle

Probably a V8 Sierra. Is it possible to unbolt the converter and then rev the engine or will I end up breaking something? But judging by the symptoms, I'm pretty convinced it's not the converter. Or at least there's something else as well.

You can unbolt the convertor, push it back about a 1/2inch. It wont hurt anything.

 

[atomicmecha]

Re: Shaky idle

Good comments, thanks Davemc1963.

No fault codes.

I've checked that the wires are properly installed several times. But wouldn't hurt to check once more. And no, I haven't checked the resistance, after all they're brand new, but you never know. They were one of the cheapest sets at Rockauto I thought of buying another set and changing them one by one.

Sorry, I didn't understand what you meant by "small coil sub harness".

And no, I haven't checked the fuel pressure either, haven't got a proper gauge.

One more thing I had in mind: the oxygen sensor. Can you check it just by unplugging it for a while?

you can check the O2 sensor by just unplugging it. The engine will stay in open loop mode. If the o2 has an issue, you'll notice immediately when you unplug it or plug it back in. Mine was bad and was causing a lot of the issue on my truck without any codes. Unplugged it and it smooth right out and would actually run better. Plugged it back in and the rumble in the idle came back. Replaced it and it runs better. Not perfect yet, but I have some more stuff to go over.

 

[Pertti K]

Re: Shaky idle

Measured the wire resistances (didn't take them off the truck though): 7,5 to 10 kohms, coil wire 4. Added a supplementary ground and took it for a ride. Idle as bad as before if not worse. But now it starts stuttering like a maniac as soon as boost starts building up. Exactly same as when I had the major vacuum leak. Damn.

 

[Jimmy]

Re: Shaky idle

Do you have a boost gauge? If you do,what's the vacuum @ idle?

Is the big vac port on the back of the TB sealed off?

The throttle stop bracket,is it straight? Those bend like marshmallows.

 

[Pertti K]

Re: Shaky idle

Drove to work with the oxygen sensor unplugged today, no change. I only have the stock boost gauge and it shows 8ish psi at idle.

Need to check the other stuff later. Thanks guys for the help!

 

[gringo76]

Re: Shaky idle

Drove to work with the oxygen sensor unplugged today, no change. I only have the stock boost gauge and it shows 8ish psi at idle.

Need to check the other stuff later. Thanks guys for the help!

8 psi at idle? I have you checked map sensor?

 

[Pertti K]

Re: Shaky idle

I guess not. How do you do that?

 

[liquidswords88]

Re: Shaky idle

When I bought my ty it ran the same way. Turned out it had a 1 bar map sensor on it. The firing order was wrong as well. A quick test you can do on the fuel pressure/pump. Find the rubber section of the return line. When the truck is running pinch it with a pair of pliers, do not close it off just pinch it a little. This will raise your fuel pressure. If the idle cleans up your regulator could be bad. If the pump starts to howl in pain, the pump could be bad. I know this method is not scientific but it will work in a pinch, get it a pinch. Lol.

 

[Pertti K]

Re: Shaky idle

I'll keep writing this"blog" so I can check what I've already done when I'm still banging my head against the wall one year later.

Yesterday took my friend, who is a GM transmission expert, for a ride. He was pretty confident that there is no converter issue. Also did the "compression test" liquidswords88 suggested. Nothing. Changed the fuel filter to be sure and ordered a cable for datamaster.

Today took the ol' reliable '49 Olds to work. Run perfect after 5 months of standing still. Some therapy was needed...

 

[liquidswords88]

Re: Shaky idle

It sounds like you have a high load low rpm misfire. Very often caused by ignition. Is it possible you cracked the porcelain on a plug when changing. Obviously due to the access on these trucks it is very easy to do and not realize it. All it takes is having the socket a little crooked and trying to tighten the plug. What does not make sense is that it ran fine before parked, or that's what I assume at least. If that is the case than the timing,firing order etc must be right. Possible bad fuel injector? You can measure the resistance of each injector. You can also pull the fuel rail and crank the engine and see if all 6 are spraying. Obviously gas will shoot all over, but it can be done. If you really want to fix it you need to go down the list and check everything off. That will require you to buy some tools you are missing. A cheap fuel pressure gauge is only about 25.00 American. When trying to trouble shoot faults a guess or an assumption will have you working in circles.

 

[Pertti K]

Re: Shaky idle

Yes it is possible to have a damaged plug. Already ordered a new set plus ignition module. I'll change the plugs one at a time when I get them. Also did spray start pilot to point out any vacuum leaks. No such luck.

At least I't trying to make educated guesses ;-) Quite a bunch of possible causes has been ruled out already.

 

[Pertti K]

Re: Shaky idle and misfire

Re: Shaky idle and misfire

Checked and changed the plugs again, at least visually they're all fine. And changing the plugs did nothing.

It's been couple of weeks that I've done nothing for this, but now I got myself a ALDL cable and TunerPro RT software. I already had the truck on idle for 10 min with TunerPro recording. I'm not able to go driving at the moment. What recorded items should I check and on what level should they be? Or is there a list of "normal" readings for a stock truck somewhere?

 

[gringo76]

Re: Shaky idle

is there some where you can get the injectors checked? If so it is usually pretty cheap and they can clean and flow check them. little bit of a pain in the ass to get them out but seems like you have covered the ignition side of it.

 

[jusssi]

Re: Shaky idle

Well, all that sounds like in my truck's symptoms. I've tried to solve it for few yers with no goal.