Rpms not dropping - 986 Forum - The Community for Porsche Boxster & Cayman Owners

gikser · 07-02-2011, 08:17 PM

Hello there i have a 2000 boxster s and when driving and letting off the throttle especially between shifts the rpms stay hung up at whatever rpm i was cruising at. Its alot more noticeable with the ac on. I tried pulling codes but have none relevant to this problem. I took the throttlebody out and cleaned it as well as the maf but to no avail. Ive tried searching on here many times but cant find an answer. Im stumped. I also thought maybe the iac is going bad but there isnt one on the throttlebody with e-gas. Has anyone run into this before?

j.fro · 07-04-2011, 05:00 AM

I've got the same thing happening with my car, and I've also cleaned thoroughly with little result. Hope a solution comes along!

gikser · 07-04-2011, 06:18 AM

Hopefully someone has an answer

gikser · 07-04-2011, 09:19 AM

someone please!!! today it rev'ed up to redline when i stepped on the clutch had to turn the ignition off and restart the car.

RandallNeighbour · 07-04-2011, 09:47 AM

Not to insult your intelligence, but have you checked the pedal to see if it's sticking? Is your floor mat jammed up next to it?

Sometimes, the most obvious things are overlooked. Since you didn't mention you checked these things, I thought I'd mention them.

gikser · 07-04-2011, 01:09 PM

No offense taken. But i have no floor mats and i pulled on the pedal to see if it made a difference and no difference.

evomind · 01-28-2014, 01:12 PM

Sounds like a dirty or failing MAF to me

uladzislau · 01-28-2014, 01:46 PM

Quote:

Originally Posted by evomind

Sounds like a dirty or failing MAF to me

I'll drop in a new one in a few days and will let here know if it resolves the issue or not. Thanks!

snakebite · 02-01-2014, 12:53 PM

I don't own a Boxster but was thinking of buying one. Anyway, I was reading the owners manual and remembered about automatic speed control. Don't know if it's related but it seems to fit . From the manual:

"With the speed control system engaged, the
engine speed will not return to idle when re-
moving the foot from
the accelerator pedal"

uladzislau · 02-01-2014, 01:04 PM

Quote:

Originally Posted by snakebite

I don't own a Boxster but was thinking of buying one. Anyway, I was reading the owners manual and remembered about automatic speed control. Don't know if it's related but it seems to fit . From the manual:

"With the speed control system engaged, the
engine speed will not return to idle when re-
moving the foot from
the accelerator pedal"

Hi! Thanks for the advise but this is not the case. Speed control is essentially "cruise control" feature that I do not have have in my car. I'm gonna drop a new MAF today and see if this fixes the issue.

On a side note I've found that turning off AC helps a lot with the issue. I remember somebody with the same issue already found this side effect. Interesting.

thstone · 02-01-2014, 01:16 PM

Quote:

Originally Posted by uladzislau

Hi! Thanks for the advise but this is not the case. Speed control is essentially "cruise control" feature that I do not have have in my car. I'm gonna drop a new MAF today and see if this fixes the issue.

On a side note I've found that turning off AC helps a lot with the issue. I remember somebody with the same issue already found this side effect. Interesting.

The ECU will increase the idle speed when the A/C is on to account for the additional load and keep the RPM's at the normal level. This seems to accentuate the problem that you are experiencing.

uladzislau · 02-01-2014, 01:17 PM

Quote:

Originally Posted by thstone

The ECU will increase the idle speed when the A/C is on to account for the additional load and keep the RPM's at the normal level. This seems to accentuate the problem that you are experiencing.

Good point, thanks!

RandallNeighbour · 02-03-2014, 06:44 AM

The cracked oil filler tube is a common problem... And a pain to change out too.

I hope you figure out your problem. Sounds like you've discovered others along the way...

uladzislau · 02-03-2014, 09:26 AM

Quote:

Originally Posted by RandallNeighbour

The cracked oil filler tube is a common problem... And a pain to change out too.

I hope you figure out your problem. Sounds like you've discovered others along the way...

I've got the new tube and tools for taking the spring loaded clamps. I read that it's PITA to change but will have to anyway. Better to find and fix it sooner than later ;-). Thanks for follow up and all the suggestions guys! The new idle control valve is on its way, I'll install it hopefully tomorrow or day after and will let you know.

uladzislau · 02-05-2014, 07:29 AM

Well it's not the idle control valve either. Dropped a new one yesterday and today I've got the same RPM issue on my way to work. This was my best bet. So the last thing to try is the AOS I guess. And the oil filling tube which is cracked in my case. Will keep working...

uladzislau · 02-06-2014, 02:33 PM

No I don't think this is AOS. AOS is connected after the throttle plate and bypass MAF. When I was logging MAF reading while driving I have seen that when the RPM get stuck the MAF sensor reports airflow (and the throttle position is closed at the same time). If somehow air would be leaking through AOS I should not see any MAF readings too. The ICV was my best bet but with the new one doing the same thing I don't know where to look next...

Steve Tinker · 02-06-2014, 06:35 PM

Something doesn't add up here - you say that when the rpm is stuck (open I ssume) you are seeng air flow across the MAF but the throttle position is closed at the same time!!

(I'm playing devils advocate here). If thats the case, then air flow is passing the (supposedly) closed throttle body - which isn't fully closed as the engine would not run at high revs with the it fully closed. So could there be a problem with the throttle body (I know you've checked, but..)?

I'm also assuming that fuel delivery is controlled by the throttle body position, so if it is sticking open you will still get fuel through the plennum. If its not sticking open, hows the fuel entering the engine ???
Can you check your fuel trims when this problem occurs.

uladzislau · 02-07-2014, 12:57 PM

Quote:

Originally Posted by Steve Tinker

Something doesn't add up here - you say that when the rpm is stuck (open I ssume) you are seeng air flow across the MAF but the throttle position is closed at the same time!!

(I'm playing devils advocate here). If thats the case, then air flow is passing the (supposedly) closed throttle body - which isn't fully closed as the engine would not run at high revs with the it fully closed. So could there be a problem with the throttle body (I know you've checked, but..)?

I'm also assuming that fuel delivery is controlled by the throttle body position, so if it is sticking open you will still get fuel through the plennum. If its not sticking open, hows the fuel entering the engine ???
Can you check your fuel trims when this problem occurs.

Yes, I know. That's why I'm asking some advice for you guys

. Can't figure this one on my own. There is only one way to bypass the throttle plate and get air flow into the body - via the idle control valve. I'll keep digging, will log everything while driving and will try to analyse the data to see where the problem can occur. I found a few forum posts about exactly the same issue but non of them provided any solution or pointed to the problematic area.

Thanks!!!

epapp · 02-12-2014, 12:58 PM

Has someone actually SEEN the throttle body closed while you are driving and shifting gears? Like, keep engine cover off, passenger stares at throttle body while driving? If its revving up and NOT stumbling or missing while shifting, then it is probably getting proper air and gas, which could only mean ICV (unlikely it can provide enough air flow for redline/high RPMs), or throttle body.

How much flow across the maf are you seeing when the problem happens? The same flow as intended full throttle on the pedal? That answer should debunk a few myths here

uladzislau · 02-12-2014, 02:09 PM

Quote:

Originally Posted by epapp

Has someone actually SEEN the throttle body closed while you are driving and shifting gears? Like, keep engine cover off, passenger stares at throttle body while driving? If its revving up and NOT stumbling or missing while shifting, then it is probably getting proper air and gas, which could only mean ICV (unlikely it can provide enough air flow for redline/high RPMs), or throttle body.

How much flow across the maf are you seeing when the problem happens? The same flow as intended full throttle on the pedal? That answer should debunk a few myths here

The engine runs just fine, no power loss, revs up as usual. I don't think there is lean/rich mixture problem here. Now, the throttle plate does not get stuck otherwise I would redline the engine the second I press the clutch pedal. Rather it's get a little bit of air in to keep the RPMs around 3K when engine is not under load. It totally looks like ICV porblem but I have swapped the ICV already for a new one and the problem persisted. Actually engine's idle became less stable with the new one so I cleaned and swapped back the old ICV yesterday.

MAF registers very little air flow when RPM get stuck, of cause not the same airflow as while I'm driving. Again, if the throttle plate would be stuck I would redline and fry the engine in seconds while shifting

.

Thanks for the reply, still digging in.
I'm investigating AOS/oil fill tube now...