2.7L Rough Idle Diagnosing [SOLVED]

So for the past few weeks I have been trying to diagnose a rough idle that has developed on my 99 2.7L Auto. While in Drive at a stop light with the brake pressed, my idle speed will drop to around 640RPM and the truck will begin to shake. This is not a violent shake, but enough to make parts of the dash rattle and be very annoying. With the truck in park or neutral, the shaking goes away and the idle increases to around 700-750RPM. This only occurs after the truck has warmed up, meaning it is in closed loop.

LINK TO SOLUTION

I have done the following so far:
Cleaned MAF (with MAF cleaner)
Cleaned Throttle Body and IAC (with throttle body cleaner)
Air filter 20k miles ago
spark plugs and wires 20k miles ago
PCV valve is good

Immediately after cleaning the throttle body and IAC I noticed the truck wasn't shaking any more at a stop light. However, after about 20 miles of driving, the shaking returned. I decided to go about this in a more technical way and started reading the LTFT (long term fuel trim) to see if there was anything that it could tell me. When I first checked the LTFT was sitting around 12-15%. I read a post by @BamaToy1997 that said this could indicate a small vacuum leak, among other things. I then decided to pull the EFI fuse and reset the system. Once I did that the LTFT dropped back into a normal range. I have attached a screenshot of my readings (RPM was 640). It will take some driving before I can see if cleaning the IAC and throttle body made much of a difference, however the shaking is still there.

A small vacuum leak is definitely possible since most of my hoses are old and can easily start to tear at the nipples. I am going to start going through and replacing them when I get a chance.

NOTES:
-I do not have a CEL
-There was an incredible amount of gunk on the engine side of the throttle body and intake runners. I only cleaned the throttle body and did not have time to pull the intake runners to clean them.

Does anyone have any more insight into this issue? I know my RPM readings are within spec, but the shaking/vibration is definitely more than what it should be.

 

I don't have too much to add. But have you had the truck stall at all?

I have the truck idling a little low. And intermittently (after it's warmed up) when I attempt to start it, say I've driven to work, then home and then back to work, when I get in to go home at the end of the day, it will start up and then stall out 1-2 seconds later. Because of the fact that it only happens when the engine is warm, I'm thinking the symptom is temperature related. Just not sure there.

I'd definitely like to find out why yours is idling low. Mine is idling below 750 as well.

 

No, mine is nowhere near stalling. Everything seems to run fine, it just shakes at idle while in drive. This is obviously because the torque converter slows the engine down and drops the RPMs. But that shouldn't cause it to shake.

 

When was the last time the valves were adjusted?

 

They have never been adjusted. I am currently at 174k miles.
Since I have a slow valve cover leak I am planning on having them checked and adjusted at the dealer whenever I can take the truck in.
Do you think the valves could cause this type of vibration?

 

It is possible. Temperature rise causes valve clearance to decrease. Valve adjustment is overlooked by many.

 

Checking the valve clearances is pretty easy, but adjusting is not (bucket/shim type valve train).
Dealer will charge around $800 to adjust, so make sure they need it first.

 

Check the egr is functioning correctly

 

I had a car that would do this and it turned out to be a transmission torque sensor,

 

O2 sensor did this to me on a truck a few years back. Chased that sucker for months, until I found an old school mechanic.

He looked at the output numbers on his fancy snap-on, and said the numbers were within spec although it wasn't throwing a code, but they were right on the lean end, causing the stumbling.

I'd suggest you find your own old school guy and get him to look at the raw data.

 

So I noticed that I now have a pending P0402 code. I'm guessing reseting the ECU caused this to show up. I still don't have a CEL but I will keep checking.

My O2 voltage jumps between .1v and .85v constantly. Is this normal?

I have also had an exhaust rattle that I have not been able to pin point. I am leaning towards a bad cat, but I have still not pulled it to check.

 

That code can cause the rough running, from what I've read. Sounds like the right path to follow.

 

http://www.customtacos.com/tech.old...06toyrm/06toypdf/06rmsrc/rm2006ta/0050034.pdf

 

So I pulled my cat off today to inspect. You can see from the pictures that light passes through and it is not clogged. It does, however, make a small rattling sound when I shake it. It sounds like there are small pieces of metal (smaller than a tiny screw) loose inside.

 

P0402 - Exhaust Gas Recirculation Flow Excessive Detected

This is either a faulty EGR temp sensor or the EGR valve itself can't close all the way (causing a vacuum leak, therefore a rough idle).

If its the valve, you could remove it and clean it up (deposits/grime could be preventing it from sealing), or just replace it.

 

Here is a graph of my O2 sensor readings over time.

Red is sensor 1, green is sensor 2

 

I finally had a chance to track down an exhaust leak. I got a piece of pvc that fit in the exhaust pipe and duck taped it to an air nozzle with 20psi going through it. It ended up being the joint where the EGR pipe connects to the LCE header. Ever since I put in the LCE header I have had issues with this joint. I may have bent the flange on the EGR pipe when installing the header. Either way, I'm going to fix it with some high temp gasket maker.

I'm sure this will have some affect on my idle issue, but it won't completely solve it.

 

Am I correct in assuming that this proves my rear 02 sensor is bad? I now have a stored P0402 code.

 

So I tested the resistance on the rear oxygen sensor and got 14ohm, which is in spec.

I also checked the egr modulator and confirmed that it is working properly.

Unfortunately, it is not possible to unscrew the egr temperature sensor without removing the egr valve. There just isn't enough room to turn a wrench. I could probably do it with a slotted o2 sensor socket, but I don't have one. I did check resistance of the sensor and got 227k ohms which is not a short (200 or below), but it seems way above spec. I also haven't pulled the VSV since it's in a tight spot. the P0402 code has not come back since clearing it, but I don't think I have driven enough. The truck still vibrates at idle.

Summary is that I have narrowed it down to one of the following:
EGR Valve
EGR Temperature Sensor
Vacuum Switching Valve (VSV) for the EGR

The cheapest thing is VSV, but I would still like to try cleaning the temp sensor first.

 

I also have a '99 2.7 and was able to remove mine using a 14mm brake line wrench.
Not much room, but was able to break it loose with the wrench, then back it off with my left hand.

Here is a photo with the wrench on the sensor, getting ready to remove it.



I hope this helps