Ok... where to start.... I just got this truck, and I have been having some problems with it. I started off having a odd surge with a part throttle down shift. The truck would shift down fine, and hold the RPM's fine, just wouldn't accelerate for a few seconds, and then the engine would surge back to life, pulling very strong. Took it to autozone and had the codes pulled.

Both banks were lean, and I have 2 with the EGR(insufficient flow and something else, i forgot). any ways, I did a little searching here, and figured that the MAF could cause the leaning out and surging. Replaced the MAF and the TPS(had a dead spot right off idle that would kill the truck)

Anyways, after i replaced the MAF, the truck literally ran like crap..... It wouldn't hardly idle. Im kinda thinking i got a bad MAF.... Autozone said they would have another one in tomorrow. just to make sure that it is the MAF, I have been checking for a vacuum leak, checked the PCV hoses, and the rubber elbow, doesn't feel like it is leaking at all. If I unhook the MAF, it runs A LOT better. I tried to clean it, and had a slight improvement(it would idle at around 550 RPM)however, after about a day, it was back to running like crap(idle falls to 400-450 RPM in gear, truck would surge, and low power)

Any thoughts on this?

 

well, I guess I was wrong about the PCV system..... the hard plastic hose that connects the rubber hose(from the MAF) to the drivers valve cover was broken off.... apparently, the previous owner saw this, plugged the tb side, and left the valve cover side open to atmosphere. 8t is rather difficult to see some things in this engine bay, as everything is covered with oil(ront eal is bad) would this hose cause the messed up idle an what-not?

 

Yes it could screw things up, not to mention the crap you could get under the valve cover. To fix it use whatever you can other than a stock PCV system. It only comes as one piece from the dealer and costs an arm and a leg. You can use just plain hose that isn't susceptible to oil breaking it down and you can use either plastic or metal hose barbs to connect it to the other pieces. When I started reading this the first thing that came to mind was vacuum leak, fix all that PCV plumbing then reset the ECU and see what happens after a few days of driving. Also note only the P side gets a PCV valve, the D side is just plumbed into the tb.

 

well, after a little thought, it looks like the hose is there so the maf sensor can constantly meter the air it is drawing through the crankcase.... with the passenger side detached, it is pulling in unmetered air. I have some silicone hose that I'm going to use tonight when I get home to repair it. hopefully this will fix it.... if the pcv system screwes up anymore, I'm cappin the intake end, an puttin in breathers on the valve covers....

 

**UPDATE**
well.... guess what... the drivers side hose appears to be a part of the PCV system and is important to overall engine running, lol.... I think that my guess about the drivers side hose being there for the metering effect is correct. i got it plugged back in after work, reset the computer(unhooked neg. cable for ~30 min). Initial impression is truck runs like a$$(idled horribly, stuttered, stalled, hesitated, basically ran only on idle and full throttle)....drove it around town here(about 8 miles all together), and it cleared up.... didn't miss a beat at light throttle, however, the idle was a little rough(500 RPM), but, I don't expect it to run as smoothly as the 1.8T in my VW, also considering the truck will be at 225K miles by the end of the week.

Thanks for the help galaxie641! Tomorrow is going to be spent cleaning the PCV valve(or just replacing it) and cleaning the IAC. I'm gonna make a good running truck outta this thing yet, lol!

 

I'm back.. and not with good news... The plot thickens, lol
The truck continues to run badly, but only when the engine is cold... once it's up to full temp, it clears its herky-jerky running.
To be clear, what has been done so far -
Replaced MAF, TPS, Air filter
Checked and repaired PCV system
Reset computer

The truck basically doesnt want to run when its cold, any throttle under ~2/3 will allmost stall the vehicle out, when up to full temp, you can drive it like a little old lady, accelerating from a stop to 15 mph in a full block, and it doesnt miss a beat!

Im starting to think of just replacing the CTS and AIT sensors. any thought?

 

Replace the IAC (idle Air Control valve). Sounds like it is sticking closed.

You also need to run it with a live data scanner to see what is really going on instead of just throwing parts at it.
Might be worth an hours labor at the dealer to properly diagnose the problem.

 

I'm gonna take the MAF back to autozone.... it was re manufactured, they admitted that they have had issues with ones not working properly in the past. the running badly showed up IMMEDIATELY after replacing the MAF. If I spray it off with electrical contact cleaner, the truck runs a little better....

On my drive home from work tonight, it took everything to keep it running for the first few minutes of driving. I really don't think that the IAC can kill the engine at anything but full throttle, and, yes, the idle actually does drop from 1200 to 900 and then to 550. it will stay idling in gear when its cold, but doesn't sound real happy. Try and accelerate, and the thing about stalls, you have to basically drive it either floored or idling..... Again this began happening only AFTER the MAF was replaced. O, yea, if you unplug the maf, runs fine(except for a slight hesitation, but its only evident with the slightest of throttle, basically opening the throttle plate before the PCM knows that its off idle)