Yet again, another long post, sorry for the detail but I figure my experience may end up helping someone later: I had problems with an intermittent rough idle for several months. Plugs replaced at 80k or so, and they were still clean. Over time, I had sprayed the throttle body intake and throttle plate with the correct and safe cleaner. I cleaned the assembly off as best as I could but it's hard to get down into the adapter area, and I had also sprayed the MAF wire gently with electronic cleaner. Not much improvement, so I started looking at things like the EGR valve. I noticed when I applied manual vacuum to it that the valve didn't move, and upon removing it, I found the valve to be stuck and completely caked up with carbon. I just replaced it and tried to clean out the opening to the lower part of the intake, but that didn't help much, so I finally bit the bullet and pulled the entire throttle body and adapter off of the intake manifold. I completely cleaned the entire assembly. Some things I noticed that might help you if you end up doing this job:

It takes about two hours to remove, throughly clean, and reinstall the throttle body and adapter assembly. You need to be very careful with not losing any of the bolts or nuts down between the intake runners, place a rag around the base of the adapter/intake area to catch anything that falls.

I noticed during the cleaning of the adapter piece that the egr port runs from the driver side of the adapter to the underbody of the adapter and empties directly down into the intake from there. I gets really caked up with carbon (at lease mine was at 98k miles). Use a long piece of wire and a small wire brush to get down into the bends of that runner and carb cleaner to open it up and remove as much carbon as you can, there's no way you will get it all. Use a lot of compressed air to clean it out afterwards.

On the throttle body itself, this is a good opportunity to really clean the throttle plate backside, clean it with a rag and the area where the plate touches the throttle throat, this will smooth out most idle problems. Compressed air will dry it out quickly. When you are done cleaning it, consider using a small spray of white lithium grease on the throttle plate spring to keep it from sticking. Take the time to torque the four throttle body bolts (to the adapter) to spec (9 nM) and use a new gasket.

Prior to reinstalling the throttle body and adapter, I took the opportunity to install a new EGR valve and a new IAC valve (this is the third IAC valve in 98k miles on the Expy and it was caked up again!). Replacing the valves now, with the assembly off, rather than after you install the throttle body/adapter assembly, not only makes it easier (especially the IAC valve, too tight behind the firewall), but it also gives you a chance to torque these components to the correct spec - IAC valve is 10 nM and EGR valve is 20 nM. Both new valves I got from Autozone had new gaskets. That EGR gasket is carbon-impregnated and requires careful torquing, just alternate tightening front and back bolt until tight at torque spec. I also added anti sieze past to the threads on the exhaust supply fitting on the EGR to make it easier to remove the large attachment nut later down the road if needed.

You can then reinstall the entire assembly right onto the manifold. The manifold-to-adapter gasket is like a reuseable rubber o-ring (white), I just cleaned mine up with carb cleaner. However, when you reinstall the entire assembly, you will need to partially insert the really long passenger side rear bolt into the back hole of the adapter assembly as you drop it down onto the intake, otherwise, the firewall overhang prevents you from dropping it down into the hole from the top. It's a little tricky to retorque the adapter-to-manifold bolts (4) to the correct torque. I did the rear driver side bolt first, then the passenger side front bolt next. Then the long bolt on passenger side rear, and then the driver side front bolt. The books says to tighten these four bolts in two stages: Stage 1: Tighten to 10 Nm (89 inch lbs.) Stage 2: Tighten an additional 90 degrees.

Another thing I noticed when reconnecting my EGR DPFE hoses (from the EGR exhaust tube) is that mine were cracked and split; might as well replace those if you get the chance, too, which I did. So, with bad hoses and a blocked up EGR valve and throttle body EGR port, I'm thinking I may have driven thousands of miles without the EGR not working properly if at all, although I never got any EGR OBDII codes on the ECM during that time, but it's working now!

I also had to replace the evaportive emissions return hose, connecting the evaporative emissions management valve to the top of the intake adapter throat, mine was was cracked and falling apart. Most likely, it was a combination of this hose failing, the EGR DPFE hose crackes and splits, the failed EGR valve, and clogged up IAC valve and throttle body that caused the bad idle. The truck runs like it is new again. Idle is much smoother and the throttle response is phenomanal. I think this job is worth doing yourself if you get the chance and can do it because you will get a better sense of how important it becomes to clean the throttle body assembly and associated parts thoroughly on a vehicle that is approaching its first 100k miles. Least I know it got done right and the results were worth it. The only other two jobs that might be useful down the road will be replacing the injectors and COPs eventually, but they seem to be working fine at this point.

 

Great writeup, thanks!

 

Another thing I noticed when reconnecting my EGR DPFE hoses (from the EGR exhaust tube) is that mine were cracked and split; might as well replace those if you get the chance, too, which I did. So, with bad hoses and a blocked up EGR valve and throttle body EGR port, I'm thinking I may have driven thousands of miles without the EGR not working properly if at all, although I never got any EGR OBDII codes on the ECM during that time, but it's working now!


I also had to replace the evaportive emissions return hose, connecting the evaporative emissions management valve to the top of the intake adapter throat, mine was was cracked and falling apart. Most likely, it was a combination of this hose failing, the EGR DPFE hose crackes and splits, the failed EGR valve, and clogged up IAC valve and throttle body that caused the bad idle. The truck runs like it is new again. Idle is much smoother and the throttle response is phenomanal. I think this job is worth doing yourself if you get the chance and can do it because you will get a better sense of how important it becomes to clean the throttle body assembly and associated parts thoroughly on a vehicle that is approaching its first 100k miles. Least I know it got done right and the results were worth it. The only other two jobs that might be useful down the road will be replacing the injectors and COPs eventually, but they seem to be working fine at this point.

Pardon my ignorance, but what EGR exhaust tube? And evaporative return hoses? It sounds obvious, is it?

 

Nice write up. Sounds like something I should think about doing.

 

Great info. Mine has 120k and i think i may look in to this. Couple of questions.
1) have you seen any improvements to performance or gas mileage ?
2) any preventive maintenance that may help this from occurring ?

oh and with injectors and cops, if it aint broke---dont fix it.

 

Yeah, if it ain't broke--wait'll I get my hands on it!

 

Thanks for the information! I also found several videos on YouTube that show some of the steps necessary to do this job...

My Harley F-150 (bought new in 2001, now has 448,000 miles) has been running a bit rough lately and I recently got error codes about running lean (P0171 / P0174).
So far I have checked for vacuum leaks and none were obvious, but have done no smoke test yet.

I found a cheap smoke tester on eBay that I may buy for the smoke testing, has anybody bought one of these:
https://www.ebay.com/itm/Automotive-...r/283210079548

What you describe sounds like regular maintenance which should be performed, and given the high mileage and has never had the throttle body cleaned, it's probably time! I also don't recall for sure if the EGR and IAC have ever been replaced, so I'll replace those while I have it all apart.

 

My 2001 Harley F-150 has almost 448,000 miles.

Parts/Components which have been replaced so far:
- Torque Converter (at 55,000 miles)
- Timing chains (at 240,000 miles)
- Alternator (at 275,000 miles)
- Fuel pump (at 300,000 miles)
- Right rear axle and bearing (at 350,000 miles)

Everything else on this truck (except regular wear and tear items) is original equipment.
- All coils and fuel injectors are original.
- Transmission is original.

I add Lucas Fuel system cleaner to my gas, at least once per month, every other fill-up.