garrett1021

Hey guys sorry to bring up a discussed topic, but I have the exact same issue that the OP had in this thread here: . I randomly got an issue where at 4800 rpm, the car just hits a dead spot. It can fluctuate from making the car lurch forward and backfire, to just a lack of power for a second or two before kicking back into gear.

The issue seems to be related to the resonance flap, or at least that is what my research is telling me. I suffered from an oil overfill around 2 years ago and I have had residual oil leaking into my intake ever since. I have taken out the plenums and throttle body and cleaned them a few times, and recently noticed a slight carbon build up in the valves under the plenums. There is also a build up of carbon on the flaps of the resonance flap itself, but I scraped most all of it out and cleaned it thoroughly.

I thought the issues may be related, but now I believe I was just looking for answers where there are none.

Today, after the car has been sitting for the past month, I decided to put the intake and plenums back on and start up the car. It started perfectly fine, and so I went on a drive. For the first 30 minutes or so I didn't take it above 4k rpm and I thought everything was back to normal. The car was driving absolutely perfectly, accelerating smoothly and not acting up at all.

Then I used seafoam on it!

I injected the seafoam into the throttle body and went through the whole can, it didn't smoke at all when I was using it, but on the drive afterwards I had a few explosions of smoke out the exhaust.

I was hoping of course to relieve some of the carbon build up, and maybe (by miracle) fix this issue of no power at 4800 rpm.

The drive went great, although I did experience the lack of power at high rpm still.

An example would be I floor it in 2nd gear at 3k rpm. It accelerates and accelerates and then hits a pocket at 4800 rpm where either nothing happens, or it lurches a bit, and then 100% of the time it is like BOOM and it feels like a turbo kicks in and the car gets a MASSIVE burst of power and then it goes from 5k-7k like nothing was ever an issue.

freno a mano

I had the same problem, solved with a new O2 sensor.

garrett1021

Very interesting. I will look into it. Thank you!

garrett1021

Just walked into my garage, looked in the engine bay and noticed my o2 sensor isn't even plugged in. Thank you so much! I'll go test it now

garrett1021

I took it out for a long drive after reinstalling the O2 sensor.

The hesitation seemed gone completely in 1st,2nd, and 3rd gear. But I did notice a definite hesitation in 4th. The O2 sensor has been unplugged since I got the car 3 years ago with no issue. I wonder why recently it caused this issue?

freno a mano

I really don't know but if the car runs better with the O2 sensor reinstalled may be with a new sensor you will completely solve the issue.

freno a mano

Are you sure the O2 sensor has been unplugged since you got the car 3 years ago? May be it has been accidentally unplugged when the symptom came.

Dan Jacobs

Check the AFM if you sweep it with a ohmmeter connected I bet you'll find a hole at 3/4-7/8 throttle

garrett1021

Yes I vaguely remember making a post on the forum with a picture of it unplugged and asking what it was. If I remember correct, people told me it was the o2 sensor and that some leave it unplugged and the car runs better without it. I remember taking it for a drive with and without it plugged in and eventually left it unplugged.

Also I took the car out again today and noticed the issue is definitely still occurring. Although sometimes it goes away. I will be looking into this further

garrett1021

By AFM do you mean the mass air flow that's hooked up to the air box?

Funny story, a few months ago at a red light a Honda civic with some college guys were telling me to rev it. So of course bad judgment got the better of me and I revved it for them.

Something went awry and when the light turned green I instantly stallen the car and managed to limp back home going 20mph on the major road in my city.

I realized when I got home that my MAF had made its way out of the throttle body and was just sitting there disconnected. I hooked it back up and everything went normal again.

Perhaps the sudden dislodging messed up the sensor? (If this is even what you're talking about)

Kappi2907

Check your dizzy belt by turning the second rotor.
Typically a 964 loses power above 4000rpm if only one dizzy is working.
I know at least 5 964's with your problem caused by a broken dizzy belt.

freno a mano

Fuel pump DME?

garrett1021

Hey guys a month later and I still have the same symptoms in the car. I unplugged the distributor cap closest to the top and it doesn't spin at all, but the one on the bottom spins about 3/4 an inch left and right. I don't feel like this is an indication of a broken belt.

I have 2 different dme relays and I have swapped them in and out and it shows no improvement.

I've read that the O2 sensor only kicks in at around 600 degrees, and that anything before that is controlled by the DME. If that is the case, I shouldn't have the issue before it reaches high temps.

A few years ago I had a weird issue with my fuel pump and the car wouldn't start at all. After messing around with my relay I managed to get the car to start by manually pressing a lever inside the relay (while it was plugged in) to start up the fuel pump, and ever since then I haven't had a problem with it.

What to test next??

thanks everyone

garrett1021

Quick update, I ordered another DME relay and plugged it in. It did not fix the issue.

garrett1021

Another note: It truly does ONLY happen on wide open throttle. The issue does not happen when I go through the entire rev range pressing the gas pedal 50%-70% of the way down. It's only when I press it at least 75% at OR past ~4800rpm that it will cause hesitation and jerking.

If I accelerate past 4800rpm with the gas pedal ~50% down, and then quickly mash my foot to the floor at say 6000rpm, the car will immediately start jerking and cause hesitation.

Although if I keep on the gas, and continue to put my foot to the floor, it will hesitate for another 3-4 seconds and then act as if there were no issues all the way to redline.

EVERYTHING in the car seems 100% normal and fine except for the 4800rpm WOT issue.

What could be connected to the WOT engage at this point that would cause my issue?? hmmm....