Bucking / No Throttle after 1500 RPM.

[Ray$]

So I have been browsing many places online, multiple forums, youtube, and anywhere else I can find information. I just can't seem to get a solution for this issue, and maybe someone here has seen this in their time with these cars.

Description:
After 1500 RPM in any gear, the car starts bucking hard and loses throttle (not power) until I shift out of gear and back in. Anything over 1500 I either buck (feels more like a sudden drop in power but she definitely jerks) or lose throttle completely and it is never predictable. If I shift the vehicle back to neutral and get below 1500 RPM, I can then shift into gear and ride until I get to 1500 or above. She idles a little high (1000 - 1100 rpm) which is a known issue but this has been around since before the car started acting up so I am unsure of its relativity.

[Video of the car in neutral not able to breach that 1500 mark]
https://www.youtube.com/watch?v=OyBOYr9VZ0g&edit=vd

List of parts swapped with either new or known working parts:
Air Filter (New)
Air Box
ICV (replaced 07/2016 with used part)
ECU (Known working)
Fuel Filter (New)
Fuel Pump (Less than 2 months used)
Ignition Coil
o2 Sensor

Currently I have no Motronic codes (all cleared with previous work). Next item on the list is to try and replace the Distributor cap and Rotor which I have in my possession. Anyone else have any ideas or knowledge they can bestow upon me before I soon lose all hope of getting this car back on the road?

[e30davie]

Inspect old dizzy cap and rotor and report back.

[IRON-E]

As crazy as this may sound, check your crank position sensor

[packratbimmer]

Fuel supply

[e30sh]

Have you checked the throttle position switch? I've seen them stick in the idle position. It's closed @ idle / open in the mid and closed again near wot on a different circuit. As a test you can just unplug it.

AFM can cause similar issues as well as CPS.

Good luck.

[Pdxseth]

As crazy as this may sound, check your crank position sensor

+1


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[Northern]

+1 CPS or CPS gap, especially if your tach is doing anything weird.

[molna]

Seems like we both have kinda same problem, but mine cuts of at around 3k rpm, without the ivc connected the car will rev normally but car will spitt/cut when you drive it on road and give full gas. Spark plugs are black.

How did this happen? Did the car stand still a longer time or have you changed any parts?

[Kershaw]

http://www.r3vlimited.com/board/showthread.php?t=372569

Check everything mentioned in this thread.

[Ray$]

Swapped out Dizzy cap and rotor and both look super worn. Going to give her a few days and see if it takes.

To answer above concerns, fuel pump, filter, regulator and all hoses checked. Everything is either in good shape or new.

Crank position sensor changed already - no change.

Tps is a good idea if it comes back.

I'll reply within a few days with an update.

[YosemiteSam]

Also could be your AFM. Old AFM's can drop the signal intermittently when the resistor strip wears out and then the PCM cuts fuel.

[Ray$]

So I just found something odd. Tried to pull the Motronic codes (stomp test) and after the 5 Wot stomps I get......nothing. I know the computer relies on Wot to send the signal. Could this mean bad TPS? We ruled out TPS the from the intermittent problem just based of my mechanical consultants experience but maybe we need to revisit it?

Update 1: After the dizzy cap and rotor swap, car runs incredible with no issue SO FAR. The problem has in the
past gone away for several days and come back so I am not getting too excited yet.

Update 2: Did the dizzy cap on Sunday. Tuesday morning now and rather than losing throttle, I let my foot off the gas and the throttle (not the pedal) got stuck! Looks like this issue is showing itself in many forms but I am leaning towards the TPS more than ever. I unplugged it and made the trip to work safely with no issue. Going to get a new one shipped asap and will report back.

[cobraken]

I also have a misfire that sounds similar to this. I have already changed MAF, Plugs, CPS, Wires, Cap and rotor. I'm interested to see if you find a solution to the problem.

[Ray$]

I am waiting on my new throttle position switch to arrive. Once it does I will provide any more info that I can but I am doing only necessary driving with my TPS unplugged and so far so good. Part arrives on Monday so keep yours eyes out for my update.

[Northern]

So I just found something odd. Tried to pull the Motronic codes (stomp test) and after the 5 Wot stomps I get......nothing.

Only odd if it's a 173 DME (or equivalent)... lots of 153 cars out there too.