Weird issue that comes and goes

[HerThing]

The car has done this ever since I have had her, but sometimes it's a month between times, sometimes the day is plagued with it every time I start. I am tuned, but, when my tuner hooks up his computer, everything is normal and the way it was set. Its just weird, and very irritating. It does it when warm or cold, my car is an 07 STI with an AEM longtube into the fender with a Cobb catless dp and hks high power, no other mods. Oil changed every 1500 to 2k, I'm anal with maintenance. Just tried to post vid, can't from my phone, so here's a description, she starts up, isles to 750 for a second, then spends about 20 seconds bouncing from 500rpms to 1250rpms. Any ideas would be helpful! Thanks guys and gals!

 

[Spamby]

Mine did the same. It was a vacuum/boost leak.
Tune shouldn't change, it will always be the same since day one.

 

[HolyCrapItsFast]

The car has done this ever since I have had her, but sometimes it's a month between times, sometimes the day is plagued with it every time I start. I am tuned, but, when my tuner hooks up his computer, everything is normal and the way it was set. Its just weird, and very irritating. It does it when warm or cold, my car is an 07 STI with an AEM longtube into the fender with a Cobb catless dp and hks high power, no other mods. Oil changed every 1500 to 2k, I'm anal with maintenance. Just tried to post vid, can't from my phone, so here's a description, she starts up, isles to 750 for a second, then spends about 20 seconds bouncing from 500rpms to 1250rpms. Any ideas would be helpful! Thanks guys and gals!

Can you post a log? AFR's are probably hunting because of "out of range" fuel trims, but as spamby suggests it could be a vacuum leak. Check all hoses and have a boost leak test performed.

 

[HerThing]

I should look at vacuum leaks again, I went through and replaced every line and rubber coupler/boot about 5 months ago. Its weird though that it only happens either a couple days or once a month.

 

[fuji_production]

Mine did this due to bad grounds. I would beef up the grounds and get a 4 wire ground kit made out of 4 gauge wire. 2 for each head, one for the tranny and 1 for the negative terminal on the battery. the factory grounds are trash. once i did this i was in the game. I would suggest checking your maf connection as well and get some contact cleaner for the maf sensor itself and for the male and female ends of the connector.

 

[fuji_production]

of course do what other people suggested as well. boost leaks seem to be a big culprit when generally speaking

 

[Batmobile_Engage]

Spot on with the grounding issue Fuji. I'm glad you mentioned it, I almost forgot about the problems that can cause.

 

[HerThing]

Hmm. Ground issue isn't a bad idea. I'll check that this weekend. I'm going to order a new ic to tb hose as well, I put a new one on but the rubber just felt odd.

 

[Grinder34]

get a silicone one with new t-bolt clamps. Those worm gears can chew it up pretty easily.

 

[Spamby]

Spot on with a t bolt.

Don't buy name brand stuff. Get a 2.75" I. D . Hose by about 3 or so Inches long.

Just google silicone hoses and you can find them for 3 or 4 dollars an inch.
Make sure they are 3 or 4 ply and able to withstand oils, etc. aramid I think??

 

[HerThing]

Yeah, I got it on that one, I was also thinking fuel filler hose, but couldn't find that diameter. Lol.

 

[Alin]

What spamby and grinder said! I made that switch and world of difference!

 

[HerThing]

So, played with it yesterday after I went and gave myself an early b'day present of new wheels and tires. Idk How it happened, but, both screws FELL OUT OF THE MAF SENSOR! How the hell does happen! Whatever I guess, put in New screws, did the reset this morning, running great! But, I will be doing the grounds for sure. I just don't know how I have missed the screws for so long. Just overlooked them.

 

[HerThing]

 

[Alin]

Looks great! :tup:

 

[HerThing]

Thank you very much! After a buddy slid it into something while I was gone, I had to get wheels as one was damaged pretty bad, still need to figure how he is going to help with repaint for the bumper damage, you can't really see it in the pic, but, it's right behind the rear wheel.

 

[Batmobile_Engage]

So, played with it yesterday after I went and gave myself an early b'day present of new wheels and tires. Idk How it happened, but, both screws FELL OUT OF THE MAF SENSOR! How the hell does happen! Whatever I guess, put in New screws, did the reset this morning, running great! But, I will be doing the grounds for sure. I just don't know how I have missed the screws for so long. Just overlooked them.

Yeah, that'll do it. :lol: Glad you got it figured out.

As for the grounds, if/when you get around to checking those, get a wire brush and some dielectric
grease. Clean up any corroded terminals and apply a thin layer of grease if necessary.

 

[HerThing]

Got it!