Scary acceleration problem

alniki · 02-08-2010, 06:38 AM

My newly rebuilt 3.2 developed a problem not unlike that of the recent case of Toyota.

Occasionally after let go the accelerator pedal and expect the car to slow down, the engine nevertheless keeps reving for up to one second and the car continues to go on at the original speed. It always occurred above 4000 rpm and after I stepped on the clutch pedal in a rush to avoid possible accident, the engine would, as expected, shoot to 5000+ rpm before the rpm went down.

This is scary and my wrench has checked the linkage from the pedal to the throttle but everything looked just fine!!

Could this be a problem of ECU, the Motronic box under the driver's seat? Thanks!

twistoffat · 02-08-2010, 06:52 AM

Does your car have cruise control?Depressing the clutch would drop the revs unless you hit the gas pedal at the same time
Nice place Taipei. Crazy driving though and I´m sure the import Tax on it wasn´t cheap. Is inhouse19 still going strong?

dtw · 02-08-2010, 07:01 AM

Quote:

Originally Posted by twistoffat

Does your car have cruise control?Depressing the clutch would drop the revs unless you hit the gas pedal at the same time
Nice place Taipei. Crazy driving though and I´m sure the import Tax on it wasn´t cheap. Is inhouse19 still going strong?

Disagree. Removing load (clutch) from an engine will result in spike in revs if the throttle is open. Sounds like a stuck linkage somewhere.

Disconnect the cruise control cable and drive around a bit, see if the problem goes away. If it does, some problem in the cruise system is holding the throttle open when it shouldn't. If the cruise isn't toggled when these problems are occurring, I am guessing it is as simple as a misadjusted and/or binding cable.

kodioneill · kodioneill's Garage

Cruise control cable bracket at the throttle body is broken.

DW SD · 02-08-2010, 09:42 AM

Take a look at the pedal cluster. Things are tight enough in there that it could cause a problem.

Doug

Rot 911 · 02-08-2010, 10:02 AM

Quote:

Originally Posted by kodioneill

Cruise control cable bracket at the throttle body is broken.

Agreed.

dw1 · 02-08-2010, 10:05 AM

+1 on checking the pedal cluster.

Pedal shaft & bushing wear is a common problem.

Tech article:
Pelican Technical Article: Pedal Cluster Rebuild

OttawaDave · 02-08-2010, 11:49 AM

I used to get a surging idle problem in my old winter beater, a '91 318i. The issue was a bad rubber intake boot and a whole mess of leaking vacuum hoses. If you check all the linkage issues that have been raised here, and still find nothing stuck, check the condition of your rubber boot and all the associated vacuum lines.

With my 318, the main problem was a hunting idle, but after cruising at a steady speed for a while, the symptoms are more of what you described...like the thottle was stuck.

Good luck!

burgermeister · burgermeister's Garage

Quote:

Originally Posted by kodioneill

Cruise control cable bracket at the throttle body is broken.

+2

Cable slips out of bracket when throttle is opened, and catches trying to slip back in.

There is probably a random hole in the air duct from the engine compartment blower fan. It's supposed to have a clip in it that holds the cruise cable, keeping it from breaking. A coax cable clip from home depot works well as a substitute.

alniki · 02-08-2010, 04:34 PM

Gentlemen, thanks a lot!

Cruise control was my first suspect but we just disabled the vaccum line without knowing the problem could be in the bracket, think I'll check that first.

Quote:

Originally Posted by twistoffat

Nice place Taipei. Crazy driving though and I´m sure the import Tax on it wasn´t cheap. Is inhouse19 still going strong?

twistoffat, crazy driving seems to be a trait of big/crowding cities. Visiting Boston, MA, USA some 20 years ago, I was much impressed by the way and speed they drove even on the main street and, some 10 years later, I had a similar experience while strolling in a residence area of London, UK

But we are nothing without an autobahm when it comes to truely high speed

Jesset100 · Jesset100's Garage

Just thinking aloud... one return spring for the throttle to close the butterfly and another spring to return the linkage to idle position.

sig_a · 02-08-2010, 07:31 PM

I was coasting in neutral while heading down a long hill (another story) when suddenly the cruise control kicked in and engine instantly ran to 7000 rpm. After fumbling around/thru the turn signal stock, I got to the key to shut down engine. Removed the complete system the following weekend. Don't miss it one bit.

bergmeister's got the most likely solution short of removing the entire thing.

ted · ted's Garage

I had a bad vacuum leak that did just what you mentioned.
Lift gas car delays return to idle.
Mech filled intake with smoke, smoke came out where a vacuum plug was mia.
Cheap fix that time.

alniki · 02-08-2010, 10:20 PM

Quote:

Originally Posted by ted

I had a bad vacuum leak that did just what you mentioned.
Lift gas car delays return to idle.
Mech filled intake with smoke, smoke came out where a vacuum plug was mia.
Cheap fix that time.

Thanks, air leaking in through the intake duct sounds like a possibility, I'll also check that and report the results.

tuned6 · 12:41 AM

Do these 3.2s have a deceleration valve on the intake system? I know my 3.0 has one and I plugged the vacuum line to rid myself of the system. It sort of feels like it is lacking brake horsepower with it hooked up like factory. After figuring out this was my problem and plugging the system I have seen that it is a popular thing to do. I believe it was just an emissions thing to pour excess air in the intake on decel.
The reason I say this is maybe this is was disconnected before the rebuild and the rebuilder hooked it back up? Or maybe the wrong vacuum line found it's way over to it?
Good luck.
Christopher

BTW.. I really expected to see a photo of a Toyota when I opened the page

twistoffat · 02-09-2010, 02:04 AM

I found this which was in relation to 88 to 92 models. Yours though an 87 build could be an 88 model

1989 PORSCHE 911 Recall - Recall ID 6381

sindo57 · 02-09-2010, 06:04 AM

I had something close to that probablem I would check the dme relay if you have for example mine is brand new about 2 months ago so when I shut off the car the dme keeps it on so I just tap it and it shuts off ....... On top of that you should check the three plugs that are on left hand side of the engine on top of the engine last time my car was idle hunting or rev by it self (it did both I thought it was on crack) check those to see if try are making contact the way they should... Hope this helps a bit

cashflyer · 02-09-2010, 07:09 AM

Check to see if somebody has installed a Toyota accelerator pedal.

bdisco · 02-09-2010, 07:26 AM

strange sticky gas pedal
^
Thread from last week.

kidrock · 02-09-2010, 02:12 PM

I don't have cruise control on mine, but for some reason Kodionell seems to be quite positive about this particular issue...probably speaking from experience.

A similar problem that hasn't been touched on yet, is the throttle linkage where it connects to the G50 tranny.

This is a common problem in the summertime, when a lot of guys with G50's complain about sticky throttles. Maybe something to be considered?

just my .02 cents.