Missing/rough idle...vacuum leak?
 

Here is the situation...I've got a 2000 V10 4X4, a reman engine with about 3000 miles on it. Chassis has 260,000+. All new coils, new IAC valve. I have a misfire at idle and up to maybe 2700 RPM. Above that it 'feels' like the misfire leaves, but it could be that it's there and I'm not feeling it since the RPMs are fairly high. I have a lean P code on both banks triggering the SES light.

I -think- it's a vacuum leak, but I can't be sure.

I know the vacuum system can do a bunch of things. I recently replaced the heater core and had to disconnect the lines to the blend door...put those back on, but I don't know if lines like those are interconnected to lines on the other side of the firewall or not.

Heater blend door and other heat/AC systems are working, so I think the lines on the cabin side of the firewall are OK.

My questions:
Is there an easy way to isolate vacuum leak from say a bad O2 sensor?
I've seen YouTube videos of guys spraying starter fluid on the lines to see if the RPMs increase...but spraying petrochemicals on a hot intake just doesn't really sound all that safe to me. Is that how you really check for leaks?

If it is a vacuum leak...I know nothing about the vacuum system or lines...where to start checking? How to diagnose a cracked or bad vacuum line? Where ARE the vacuum lines?

Any help you can provide would be greatly appreciated...I gotta get this rig up and running ASAP.

Thanks!

If you have a miss from a vacuum leak it is not going to be a small line. A good auto repair shop with a smoke machine can find it quickly if it is indeed that

Check to see on the air cleaner if the rubber grommet popped out where the MAF wires go through.

Had similar problems on mine. A small vac leak wont trigger a ses light. Though a did find a couple of small leaks I repaired.

O2 sensors are cheap also. I would have changed those when a new motor went in. Whats the milage on them?

I'm gonna assume 250k+...? I've never replaced them.

I did a quick peek last night and didn't see any obvious hose issues, but honestly I don't know what hoses I should be focusing on.

Any other sensors I should be looking at?

This may be unlikely in your case, but I had an injector plug that was not completely seated/clipped and loosened on me about 3k miles after replacing spark plugs and coils. This caused a misfire and lean code. Might be something easy to check and rule out.

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If you're getting P0171 & P0174 Bank 1 & 2 Lean, it is most likely something to do upstream of the O2 sensors. It would also mean something upstream of the banks themselves. What is upstream of the banks? You have the main intake tube which can crack or have a loose clamp. You have the MAF which can be dirty or have failed, and you have the grommet for the wire bundle as mentioned before. Check that all the connections are tight and cannot move with your hand.

If you have a OBD2 reader, you can read the MAF readings and see if they are out of spec. Most of the time a cleaning with MAF sensor cleaner will help that out.

Other major vacuum lines which could cause this are the PCV hose coming off the passenger side intake manifold. make sure it is tight and the hose (especially at 90 deg bend) does not have any cracks. You also have 2 larger hoses that connect around the back of the intake, one going to the IAC valve. Do the same checks there.

Do you have EGR system on this truck? It could also point to a malfunctioning EGR, but I don't have much experience with diagnostics on the EGR systems on these trucks.

Lastly, the rest of the vacuum system is designed for the 4x4 ESOF and HVAC system, and utilizes 3mm? diameter tube. Even if there is a major leak you won't get a misfire. They are the small tubes that are running on the passenger side firewall/fender area. You can actually bypass the ESOF system and have the vacuum going directly to the HVAC system, which I did since my vacuum lines down to the hubs were completely gone when I got my truck.

My Ex is at a shop right now for same thing. I did the carb spray check and looked at everything under the hood. No codes either. Got fed up and brought it in. Should be ready this week. I’ll update with what they find. I’m thinking it’s EGR or some other liberal related nonsense.

Sent it to a GOOD shop this time with a description. They put it on their super-wizard machine and found an injector fault on #6...the plastic clip lock bit had broken off and apparently it backed out enough to lose contact but not fall off. A zip tie later he called me to pick it up no charge. Those connectors are like $5 on RockAuto, so once it warms up I'll cut the broken one off and put the new one on.

...I was sweating a call saying it would be hundreds of dollars to fix something weird (or worse that the "new" motor had an issue...happy Wednesday to me!!! :-jammin:-X22

Well I got it back today after 5, that is FIVE!!!!!!, damn weeks in the shop. While it is slightly better, it’s still stumbling and popping at idle. I’m so furious right now I’m going have a beer at 9:30am.

Tried to post video but it didn’t work.

...CRB357, I'm feeling for you. I have a new SES light, P0171...so back to hunting for a solution. Need to know how Bank 1/Bank 2 aligns with which side of the engine. Is Bank 1 driver side? Passenger side?

Usually bank 1 is the same side as plug 1 which is the passenger side on our V10’s

Quick question, do you have EGR system on this truck?

I would think so...I have to get smogged every couple of years in CA...I can't imagine I'd pass without one. :)

I have pondered the EGR being the issue. Like the valve being stuck. How does one check for that?