This is probably a dumb question for the mechanics in the group

"Chairman Kaga" (mike-mckinnon)
11/07/2014 at 15:14 • Filed to: None

I replaced the air filter in my GTV6 yesterday. I honestly can't remember the last time I did. Bad me. It's just one of those parts, especially when you have a car as goofy as mine, you don't always remember to maintain. They're also sometimes hard to find, so when you do remember to buy one they aren't always available.

Anyway, long story short, after replacing it my idle bumped up from about 900, which is where it should be, to around 1500 after warming up. Cold start it was at almost 2000 revs. I just set timing and idle last weekend. Haven't done any other work since.

So my question. Could the old filter have been so clogged that replacing it opened up the engine's ability to breathe to that degree?

DISCUSSION (19)

Party-vi > Chairman Kaga
11/07/2014 at 15:17

Is it injected?

SidewaysOnDirt still misses Bowie > Chairman Kaga
11/07/2014 at 15:19

I doubt it. It's more likely that something else got thrown off. I'm not familiar with these engines, but I know that they're fuel injected, so does it have a throttle position sensor? That would be my first guess. On alot of older fuel injection systems, this needs to be aligned, and if you bumped it, it could be giving a false reading and causing the engine to run higher.

uofime > SidewaysOnDirt still misses Bowie
11/07/2014 at 15:26

could also be the mass airflow sensor got disconnected if the car has one

RallyWrench > Chairman Kaga
11/07/2014 at 15:26

The filter would have to be almost impenetrably dirty to have that large an effect, and would have affected running beforehand. Is it possible you nicked a vacuum fitting or the boot from the airbox to the AFM & idle valve was dislodged or cracked when moved?

Aaron M - MasoFiST > Chairman Kaga
11/07/2014 at 15:36

If the car uses EFI, there's likely an idle air control valve, which uses feedback from the ECU to set idle speed. If your air filter was dirty enough, the IAC would have opened further to hit the target idle, and now is open far enough that the idle is high. If this is the case, the ECU will learn out the difference after some driving and your idle will return to normal. If it doesn't go away, it's a different problem.

Chairman Kaga > Party-vi
11/07/2014 at 15:51

Yep. Bosch L-jet.

Chairman Kaga > SidewaysOnDirt still misses Bowie
11/07/2014 at 15:52

The TPS on these cars is notoriously finnicky, but it's also nowhere near the intake box. It's up on the plenum by the cold start valve. Still, worth a check.

Chairman Kaga > uofime
11/07/2014 at 15:53

Or maybe the box didn't seal well when I clamped it back down? But that's still before the MAF...

Baybe I damaged the crusty old air hose from the MAF to the throttle body. They're known to crack and leak, letting unmetered air into the system.

Might also be the potential air leak between the plenum and the manifold that I've been chasing, and is suddenly manifesting a little differently than before.

Chairman Kaga > RallyWrench
11/07/2014 at 15:55

Might've cracked the air snorkus from the MAF to the throttle body? It's original and they're prone to cracking, especially after being pried up to get to the air box clamps. All vacuum lines were connected and the hoses were new, so little chance one cracked. Still, worth a check.

Chairman Kaga > Aaron M - MasoFiST
11/07/2014 at 15:56

It's an analog Bosch L-Jet system. It does have an ECU but idle is set the old fashioned way. It uses a throttle position switch as well. Possible culprit.

Party-vi > Chairman Kaga
11/07/2014 at 15:57

Hmm. Maybe you need a new idle air controller (if it has one), or to clean your MAF.

Aaron M - MasoFiST > Chairman Kaga
11/07/2014 at 16:00

If you set the idle with the dirty filter, yeah, may still be the same effect...so long as you set the idle with a throttle bypass the principle is the same.

Trying to deal with a motorcycle with carbs has taught me I just shouldn't buy old cars.

SidewaysOnDirt still misses Bowie > Chairman Kaga
11/07/2014 at 16:14

I've never seen a vacuum leak cause the idle to go up, only go down. Also, whenever I've had a hole in my airbox or filter, I've seen the idle go all over the place, not stay consistent. I'm not saying that it's not these things as I'm by no means an expert, it's just what I've seen through my own projects and cars.

RallyWrench > Chairman Kaga
11/07/2014 at 16:17

Yep, that one. I remember they're Bosch injected but forgot if the AFM was bolted to the airbox or upstream.

Chairman Kaga > Aaron M - MasoFiST
11/07/2014 at 16:31

I'm just gonna try and ratchet down the throttle bypass and see what happens. Otherwise it's pulling stuff apart, cleaning, testing, etc. The L-Jet system is crazy simple and reliable, aside from the 1,978 potential points for an air leak.

Chairman Kaga > Party-vi
11/07/2014 at 16:35

MAF and throttle body are probably both due for a cleaning, although I doubt generally cleanliness would be a problem given the circumstances.

The idle controller is an o-ring. Either $20 from Alfa, or $.20 from Home Depot. I got a century's worth for the same price as the official part! I replace them every year but this one is brand new. I just I had the plenum off and popped in a new one. The old one was still nice and springy, but whatever. If it's apart might as well replace.

I'm leaning more toward a new leak in the snorkus or a TPS anomoly.

Chairman Kaga > RallyWrench
11/07/2014 at 16:37

Kinja'd!!!

Yep. The snorkus is the weak link.

Chairman Kaga > SidewaysOnDirt still misses Bowie
11/07/2014 at 16:38

I think I'm just going to recheck timing and reset the idle. If it's still acting goofy then I'll start pulling parts, cleaning and testing them. Woo hoo. Fun weekend of working on the car instead of driving it!

JGrabowMSt > Chairman Kaga
11/08/2014 at 00:19

I missed this. Not sure if you're still having the issue, but try unplugging the battery for an hour, and the plugging it back in and seeing what happens.

It's not really the same thing, but when installing CAI on most new cars, it's recommended (and basically a requirement) to unplug the battery. It resets the ECU so that the engine can learn to run off the better intake right away, as opposed to running poorly for a while, trying to make up for the difference in airflow.