2.7L Rough Idle Diagnosing [SOLVED]

Thanks for the pic! I only have a 10/12mm brake line wrench and I was unsure if a 14mm would fit and still be able to turn. My regular 14mm hits the side of the EGR valve. I might actually have an extra 14mm socket that I can grind a slot into.

 

You should purchase a 14mm wrench, even though this might be the only application for it. The walls of the business end are thinner than a normal box-end wrench, so it has more room.
I also soaked it in PB Blaster a couple of hours before, as well.

Good luck

 

So I was able to pull the EGR temperature sensor and clean it. I used a 14mm deep impact socket that I cut a slot in. This made it super quick and easy to remove.

It had about 1/16" of hard oil/gunk/soot on it that needed to be scraped and scrubbed off. I then tested it up to 212*F by boiling the business end in water while reading the resistance across the 2 pins. I got 14k ohms which is within spec. I didn't have an easy way to get it up to 302* though.

So I guess I am down to the VSV or the EGR Valve itself. I will try to pull the VSV this weekend and test it as well.

 

Also, here is a current graph of my o2 readings. It is a lot different than before.

 

I tested the EGR VSV today and read 38ohms across the terminals which is within spec. I did not have a chance to apply power to it to test its function though, I will see if I can pull it again tomorrow.

 

So after testing everything that I could, I did not find an engine related problem. I decided to take it to the dealer to see what they could come up with. I had a few other issues that I wanted them to check including the valve clearance. The service tech suggested that the excessive shaking is due to the rear transmission mount being bad. He confirmed that it was definitely moving too much. Since the dealer here wants $150 for just the part, I will do it myself ordering from partznet.com. I am not sure if it will completely fix the shaking issue though.

I told them to check the valve clearance anyway for my piece of mind. They quoted me around $400 if they actually have to adjust the clearance.

 

I replaced the rear engine mount (transmission mount) today. The original one was definitely bad with the rubber separating from the metal. This, however, did not remedy the vibration/shaking at idle. It made it slightly better, but it is still excessive. It is definitely something engine related.

I may pull the IAC again and see if I can diagnose it further.

 

Only happens in gear with brakes on? Have you checked brake booster for vacuum leak?

 

Yes, only happens in gear (D, R, 2, 1) while stationary. The same occurs with or without the brake applied. I can set the parking brake and it still happens. The idle speed is noticeably lower than when in Park.

The brake booster hose is old and could definitely be replaced, but there is no noticeable vacuum leak. That is the only hose correct? If there was a vacuum leak, would it affect the brakes at all?

 

Blows my theory.

 

So I decided to pull the throttle body out once again and double check everything. This time I powered the IAC with 12v following the FSM and it functioned perfectly. I did the same with the VSV for the EGR and it passed as well.

I was going to check the Throttle position sensor, but mine only has 3 contacts and the FSM for a 96 that I was following shows 4. Does anyone have the correct procedure for the 3RZ on a 99?

I am going to replace the 2 front engine mounts sometime soon since the rear one was pretty bad. I'm sure this will lessen the vibration but I still don't think it will completely eliminate it.

 

Replaced both motor mounts today. They were definitely bad, but the vibration still persists!

I may completely pull off the EGR to test it more easily, but I really don't know what else it could be. I think I have exhausted all possible issues.

 

I pulled the EGR valve today and checked its operation. The "piston" inside moved smoothly. It definitely had carbon build up and I cleaned that out, but it did not solve the problem. I reinstalled it with new gaskets, plus the gasket at the exhaust manifold.

I noticed that my VSV for EVAP was was ticking. This was like it was cycling open and closed. I pulled the hose off and took a video and it was definitely pulsing. Is this normal operation?

 

So I just held a screwdriver on my injectors to see if they were firing correctly. #2 and #3 had a strong distinct tick to them while #1 didn't have much of anything other than what seemed like engine vibration. #4 felt similar to #1 but it is hard to reach with the intake on.

Any thoughts? Could a lazy injector be the cause of this? Could it be the coil pack? My truck has 2 coils (one for 1and4 and the other for 2and3)

 

So I decided to boost my baseline idle slightly. In Neutral or Park it was running at 675-700 when warm. I loosened the throttle stop jam but and turned the Allen set screw slightly to increase the baseline to 750-775.

Now in drive while stopped my rpm drops to about 675 and there is a lot less vibration. I also noticed that the vacuum throttle stop mechanism is now perfectly even with the throttle stop. Meaning I cannot turn the throttle closed more by compressing the vacuum solenoid. Only time will tell if this will cause issues. If it does I can always adjust back to where it was.

 

I FINALLY FIXED IT!!!!!

It was suggested to me a while ago by a few people that the vibration could be coming from my exhaust. I tested this theory initially by using a c-clamp to pull the exhaust pipe toward the frame rail. This did absolutely nothing so I assumed that it was not the issue.

6 months go by and I decide to get an actual exhaust hanger and try it out. I got a 2-1/4" exhaust clamp and a hanger with a strap from advanced auto. I clamped the hanger to the exhaust and then clamped the other end the frame rail with a c-clamp. I tested a few different positions and finally found one that stopped the vibration while stopped in Drive completely. It was like tuning an instrument. The distance between the catalytic converter exhaust hangers and the muffler exhaust hangers must be some sort of wavelength that matches with the engine vibration at idle. It would amplify at that specific rpm and make the whole truck shake.

Keep in mind my exhaust is not stock. I have a Flowmaster Delta 50 welded to the stock pipe where the original muffler was. The tail pipe is cut off just before the rear axle.


So here is the combination of what worked to solve the vibration
1) new transmission mount
2) new engine mounts
3) exhaust clamp/hanger

While cleaning the Throttle Body and IAC are definitely important, those services did not do anything to affect my idle.

I now have a vibration when the rpm drops from high idle (roughly 900) to low idle (roughly 650). I'm thinking it is around 750rpm, but the truck never sits at that RPM so I am fine with that.

 

Hey Noah, My truck recently developed this exact same issue...shaking at idle. Do you have pics of how you ended up clamping the exhaust?

 

I don't have any pictures, but I just got an exhaust clamp and hanger strap and bolted it into an existing threaded hole on the frame. A good way to determine where to position it would be to use a c-clamp and try multiple locations. It ended up being almost exactly halfway between the cat hanger and muffler hanger.

 

Awesome. Thanks. I don't have any hangers there at all right now so I'm guessing that is my issue.
Thanks for following up this thread with what fixed your problem. Too many threads just end with no resolution.

 

I suggest you make the shaking occur (put the truck in drive and put the brake on). Then climb underneath and look at your exhaust. It doesn't take much movement for it to shake the whole vehicle.