Couldnt find a thread about this so if there is one please let me know. So here it is. I have a 99 f350 with a v10. The motor was rebuilt about 20k miles ago. I have an sct livewire with 5 star tunes and about 6 months ago I started getting a lopy idle. It sounds wicked but runs like garbage and fuel economy is way down. When the motor was installed I replaced everything with new Ford oem stuff.(sensors,solinoids, ect.) I have been chasing this issue with no luck. Any ideas? Cam sensor,iac,tps,have been replaced. Tunes were removed and returned to stock.

 

Hook up a scan tool and see if it’s misfiring.

— Dave

 

I have ran a scan tool and data logging trough my sct livewire. and did not find a missfire. On my data log I see some stuff that is suspect to me but I am not sure what some stuff is supposed to look like.

 

A good scan tool will show Mode 6 data which has misfire counters. Unless you have a crack in your exhaust and the lopey sound is due to low compression in at least one cylinder.

— Dave

 

Surging/Lopy idle means to me it is going up and down...is that the case, or is it more of a rough idle? If no codes present and fuel trims are within spec, I'd check for vacuum leaks. Namely at the PCV hose, 90deg location. Check plastic/rubber intake duct for any cracks, check for loose connections for any unmetered air. Not a bad idea to clean the MAF. Might want to inspect the idle air control valve. These are all shots in the dark I know, but might be helpful to try the simple things first, especially when there isn't a clear issue popping up on the scan tool.

What are you fuel trims looking like?

 

Sorry guys Been busy with work so didnt have a chance to mess with my truck or even jump online. I had a shop run a scan tool on it this morning . I dont really think they did I think the just guessed. They said my air filter needed to be replaced (k&n) and that my maf was bad. When I dropped it off I asked them to read the missfire counts, knock sensor,and my o2 readings. Also asked them to give me a print out. When I picked it up they didnt have a print out. I replaced the maf and it runs the same. I called and talked to the tech and he said no one ever said anything about missfire counts,knock sensor,or o2 reading. He said he didnt save the data log so no print out but he said he didnt see a miss fire,o2 sensors are good, injectors are good, fuel trims are good. Said whit maf plugged in he covered the maf inlet and it chocked out right off, but unpluged the maf and the idel kicked up. So he said it seamed the air flow was restricted. Maybe gummed up tb. I pulled the tb off and checked it and it looked like a 20k mile part should. Clean. Stainless long tube headers with no cracks or leaks. 4 inch metal cold air intake with no leaks. Brand new IAC,TPS,EGR,Crank and cam sensors. Cant find any vacume leaks.

 

When I view my data logs from my sct livewire there are some things that dont seem right to me but I dont really know what they should look like. I would think for instance my fuel trims should pretty much match but one bank looks a bit delayed from the other, the spark advance to me seems pretty wild and looks like a heart beat at idle and i want to say it ranged from -6 to +40. If i can figure out how to post it here I will. I am sure there is someone local that knows his stuff but I cant find that guy and every one here just wants to do ls stuff. Its not a rough idle or a surging. Idle stays smooth as far as rpm but it sounds like it has a big race cam with lots of valve overlap. Smells really rich at idle and has been getting 7-8 mpg.

 

Ok so consistent RPM but sounds like you've got a cam in there... interesting.

Still be interested in what the fuel trims are, are they consistently negative or positive?

You tried another MAF? Are you able to check the MAF Voltage with scan tool? Key On, Engine Off, you should see 0V. Hot idle should read 0.7-1.0V

How's the voltage look when idling, measured at the battery? Constant?

Do you have an EGR system?

.... more shots in the dark for me, hopefully someone else has a better reply

 

Unplug the MAF sensor and start the engine. This should force the engine into a default strategy. (You will get a check engine light). If the lope at idle is still present then the MAF sensor isn't the cause.

 

So with the maf unplugged the lope is the same. Fuel trims on both banks have a min of .82 and a max of 1.18. My spark advance ranges from -6 to+47. And I do have a full egr system. Motor ran great for about a year and about 6 months ago this started a few days after changing to a 91 performance tune. Tought it might be the tune but since then I have ran stock, 87 eco, 87 perf, and 91 oerf tunes for weeks at a time and no changes as far as lopy idle.

 

Screen shots are at verious points of a 40 min data log. Some at idle and some are at speed.

 

If I can figure out how to data log the voltages I will post those.

 

I'm no expert, but all that looks fine to me. I see your voltage readings in there too, they look solid.

I've never paid attention much to spark advance on this truck, so not sure if that is an odd range. The PCED manual states 17-23 degrees for hot idle and 38 degrees for 2500 RPM.

I think it has something to do with the tune, you might be best off calling 5 Star directly, I've heard great things with their customer service.