I've been having trouble with my truck now for the past 2 months. Its been stumbling/hesitating when it reaches operating temp. FSM says the most likely culprit was the EGR valve. After testing it, I ruled it out. Another forum told me fuel filter could be it. I replaced it because it was cheap to replace. MAF and TPS were ruled out as well. I double checked the TPS with an ohm meter and TPS is as it should be. Since it was time for a tune up anyway, I ended up getting new wires, cap and plugs. Throttle body was even cleaned out. Tranny fluid raplaced.

Someone else suggested Headgasket might be starting to go. It did overheat recently, but that was due to really dirty coolant. After flushing, replacing and observing the coolant, draining and inspecting oil for discoloration I ruled out HG because I don't have any other symptoms.

So is there anything else I missed or should I just bring it to my trusty mechanic. Any or suggestions would really be great.

 

hows the timeing ?

 

blow out the vacuum lines with compresses air, i had a little clog in my egr piping

 

Since it happens with a certain temp, I would check the water temp sensor for the ECU. The one labled in green below


This is how to check that sensor.

 

the engine coolant temp sensor (ect) could deff. be the prob. when it reads the engine is cold it tells the ecu to send alot of fuel untill it warms up. but if the sensor keeps thinking its cold and sending in lots of fuel then it could cause the symptoms you have.

 

silicon,

i changed your title. please read the thread title policy and keep your thread titles specific and on topic. you will get a better response.

bob

 

Have you checked your codes? There is not always a CEL when there is a stored code. Could be the O2 sensor. A bad one usually throws a code. There is also a simple ohm check in the manual.

 

How did you rule out the AFM?

 

O2 sensor I replaced along with my major tune up. I did this because I don't know if the PO did.

Thanks Bob, rookie mistake on my part. I apologize.

 

I'll recheck today and see what I find. I need to buy another timing light, loaned it to a friend and was not returned.

AFM was ruled out when I got an OEM unit from Toyota. I had to replace it because the old one was coming apart.

 

Sorry to hear that given the $700 plus the dealers charge for the AFM.

 

I don't recall how much, but it wasn't $700.

 

Timing is now set to 5deg. BTDC.

I took it out for a test drive to see if it dissappeared. It did not, its still there.
I'm at the point where I don't know what else to do except bring it to my mechanic.

 

Also check for leaks, spary some carb cleaner on the base of the injectors and the intake manifold gasket, especially on #4, while it's running. I'll have to rescan that pic above to make it bigger, I set the resolution at 72 pixels per inch for fast loading, and if I enlarge the file it really pixellates.

 

And how did you rule out the EGR valve? Did you take the vacuum line off the valve and plug it?

I'm chasing down some less serious but similar symptoms, and I'm pretty sure my EGR isn't closing all the way all the time. Try disconnecting it, and then tapping on it when the engine is idling to make fairly sure it's closed.

 

Is that safe? I'll test the coolant temp sensor tomorrow.

Yes, that's exactly what I did.

 

Get FSM. There are a bunch of electrical tests you can do from the ECM to check TPS, AFM and a few other things more thoroughly. There are some free ones on line. I can give you a link if you need it.

I've been having similar problems with mine. The TPS needed to be adjusted. I took care of that and the underhood tests checked out. I then did the ECM tests and found three faulty readings for the TPS. I haven't bought a new one yet because I can't affor it right now. I did unplug it and it is running fine. All hesitiation is gone. I'm sure I'll have to replace it before my next smog test but it's getting me by for the time being.

This might not be your problem but I would be curious to find out if yours does the same thing.

 

I believe you will find the AFM from the dealer, will cost more than $700 for the part by itself. That was the price 5 years ago. Higher now.

That leads to the possibility that you do not have what you think you have, with respect to the AFM.

 

Do you have that link. I have an FSM, but more info in this case would be helpful. The TPS I've adjusted a few times now thinking it was it, but it wasn't.

What did you unplug? The ECM or the TPS? I'm unclear to what it is you unplugged.

You maybe right, I'm double checking with my parts guy right now.

 

AFM cost me around $580. Retail is about $770 right now.