Rough Idle. Please Help!

[monk36]

Hey my mods are listed in the sig. I have been driving the car fine with no signs of wear, and tonight, out of the blue, I drove it home, and as I got closer to home, it started idling like I had a cam in it. I have no idea what it is, or what to do. There are no good performance shops within a 200 mile radius. The belt shows no signs of wear and there are absolutely no error codes. I'm at a complete loss on this one.

Could an exhaust leak cause this without showing a code? I think it seemed louder next to the car than usual, and that there may have been some extra air coming from the underside of the car, more on one side than the other, but I don't know what it was normally, so I can't be sure till daylight.

The accessory belt up front showed no signs of wear at all and the engine seemed to be running otherwise smoothly, no ticking or anything. The whole car shook at idle it was so lopey. Once I hit the gas it revved fine, but the rpms fell really slowly and sometimes increased for a short time.

On my drive home, I accelerated to 35 in third, let off the accelerator, and the car continued at that speed, as if my cruise control was on. It wasn't. Could this be as simple as an exhaust leak? I'm really hoping so at this point, because just about anything else would be many times the price to fix.

Please help me out. I'm at a total loss.

 

[lostsoul]

here we go..

1) check fuel pressure
2) did you use any octane boosters
3) check all the plugs
4) check air filter and all piping for loose clamps
5) could be clogged fuel filter

the 35mph thing is strange.. see if the rough idle goes away if you pop in the clutch.

I'm out of guesses

 

[Chrome61]

Clean the thottle body? it could me hanging....

 

[monk36]

I checked the throttle body, no problems there. I don't think it's the fuel, because it still runs pretty strong once going, minus some surging and hesitation. I really think its the plugs at this point. I didn't take them out, as I don't have any replacements. The plugs have about 20k on them, so it's probably time to replace them anyway. I am having 8 HT0s shipped out quick and I'll replace them when they get here.

Oh, and all piping is good, minus the air I felt under the car. I'll be switching midpipes soon though so that's a nonissue, and lol I never use octane boosters. I typically start up quick and go so I didn't notice it till it was bad. My air conditioner unit is going out, and so that's been making the idle slightly off, and I just didn't notice it getting worse. The air will hopefully be fixed soon too.

When I posted I was a little freaked out because I thought it might be trans related, but the alum flywheel I have was just increasing the amount of noise coming from there when the car was close to dieing at too low of rpms.

 

[tyler_2118]

Tps sensor

 

[monk36]

Tps sensor

If so, does it need cleaning, resetting, replacing, what? And how would you reset such a thing? I know where to find it, just not what to do.

And wouldn't that throw a code? I drove the car to work, sputtering at every stop, and not a single check engine light came on.

 

[SilentScope]

clean maf, check for vacuum leaks, check again, make sure your TB is clean and the TPS may need to be re "calibrated". ive never had to do that so i dont know how.

 

[tyler_2118]

my tps went bad and didn't throw a code until the damn thing completely went out but it acted just like yours for 2 weeks and you just have to replace it.

 

[monk36]

I just datalogged it with the xcal 3, just a plug in type deal, no wideband or anything. Here is exactly what it says.

fdpc 0.21
frp ~40
iat ~130
maf_v ~130
maf_v INVALID
spark anywhere from 10-20, fluctuating +- 5 each second
frp ~39
iat 130
mafv 115
mafv INVALID
spark about 20
fdpc .21
frp 39

I have no idea what is usual for most of this. Can anybody shed any light? Is it my maf with the INVALID or is it supposed to be like that? Is my maf a dirty whore(i'll find out for sure in the daylight)? Is the spark ok with it fluctuating that much at idle? Is the intake air temp too high? What is your favorite color?

And is there a way to test to see if the tps needs replacing?

 

[GrnBullitt08]

I have a spare TPS sitting if here if you want it. I thought it was my problem and it ended up not being that.

 

[monk36]

The exhaust sounds louder on one side than the other. Idk what that could mean, because if a pre or post cat sensor was out, a check engine light would be on. I'll check it tomorrow anyway.

 

[monk36]

First off, I'm a fucking idiot. Second, it was a vacuum leak. After checking nearly all the damn plugs this morning I got to a plug by a port close to the coolant return line. The manufacturer had said to plug up this port, that it was only used for their testing, and I had n-rigged it with a quarter and some tape. well the quarter slid down, and this morning, having driven it a little yesterday, the sucking noise was unmistakable. I'm off to the hardware store to get a neoprene plug for it, like I should have done in the first place, instead of half assing it. Thanks for the help.

 

[killr3v]

Nice.

 

[monk36]

Well it seems I spoke prematurely. I did have a vacuum leak, but that was not the source of the most problems. A few nights previous, I drove over one of the various bumps in the shitty louisiana roads. I didn't think anything of it, but apparently it tripped a fuel cutoff switch. This switch, 87 dollars later, I now know is located in the drivers side kick panel. My car died yesterday totally, and I couldn't get any codes from it. Had it towed to a machine shop thinking it was something more serious, and they had it fixed by the end of the day. I didn't have any fuel pressure at all at that point. I did earlier in the week, but I guess it was so intermittent that I didn't catch it.

So remember that. Fuel cutoff switch... drivers side kick panel. Good stuff to know.

lol The first thing that the tech asked me was if I had been offroading. I was like, what the hell did he find to spark that question? Bottom line, Louisiana roads are equivalent to a bag of shit.