Hi Everyone,

I have 98 5sp 4wd 3.4 with 250K miles. 1st owner bought new. Maintenance done by me since day one.

I am experiencing a strange thing and I looking for guidance.

When I drive long distance, over 100 miles with temps over 100F, come to a stop the engine wants to shut down. The RPM goes below the idle at a traffic light and sometimes it just shuts down or attempts to shut down but then it revs up again and stays on idle. Then it does it again until I am back in cooler temps where its all fine.

I have replaced the following:

Sparks, fuel filter, TPS, Spark wires, Air filter, cleaned the MAF etc...Timing belts changed at every 90K miles along with water pump.

I do have a scangauge installed and the highest temp the engine gets is about 204 and the temp gauge has been normal regardless of the temp outside.

This has been going on over 8 years now. Just when I drive in hot temps AC on or OFF for a long distance and then stop and go it does this.

The feeling is, the fuel stops coming or evaporates someplace when its hot. But I am open to any advice anyone can have to look into.

Thank you in advance,

Scoop.

Alright, there are 2 things to look at. First is the throttle return damper (or what ever it's called). Basically when you let off the gas completely it prevents the throttle butterfly from slamming closed. IIRC it works when the throttle is opened (loses vacuum) so the plunger extends, when you let off the throttle completely it absorbs some of the initial shock. When the throttle closes it creates vacuum and the plunger retracts to its idle position. Then the idle control valve takes over.

The plunger could be bad or have a vacuum leak in the hose for the plunger.

The second one is your idle control valve. It could be gummed up and need cleaning. It controls idle rpm's when it's idling, and will open up more letting more air bypass the throttle plate causing the bump up in rpm when the ac is on.

If you cleaned your throttle body on the engine then all that gunk and junk washed down into the idle valve. It could also just be old age too. Nothing lasts forever.

The pic is of the plunger thingy.

Here is a vid of cleaning and testing the idle control valve:

https://www.youtube.com/watch?si=wkPLHutU6Hrr9cj8&v=agIRNNA-6cs&feature=youtu.be

Attached Images

 

My car has also had this issue of shutting down while driving long distances and I had it checked out right away. It turned out to be a stuck control valve. Luckily after cleaning the control valve it worked fine.

I chased a similar problem for years on my 2000 Limited. It never happened when driving around town. The only time I had issues was on longer trips in hot weather; my truck would randomly stall once I got into stop and go traffic (or stop lights) after extended highway driving. It sucked, but was intermittent without a CEL, so it took a long time to figure out.

MAF cleaning, throttle body cleaning, new fuel injectors, a new IAC, and a new crank position sensor did not fix the issue.

A new charcoal/evap canister fixed the problem for me. At this point, I don't remember the details on how the valves on an evap canister work, but if one is failing, it can cause your truck to stall. I am sure you could look into testing the valves and replace only those, but it may be easier to replace the whole assembly and call it a day.

Interesting! I have same symptoms and just replaced the IAC with no improvement. Guess I will try canister next!