Acceleration Troubleshooting

Last updated: June 4, 1998

Date: Sat, 23 May 98 09:35:17 EDT
From: zgluszek@VNET.IBM.COM

>I've got a small problem with my 3rd gen. When I transition from
>deceleration (no throttle) to acceleration the car stumbles momentarily
>around 1/8th throttle. It also happens when I'm at 1/8th throttle cruise
>and begin to accelerate.
>The air/fuel gauge is showing a complete cut in fuel during the stumble.
>I suspected the throttle position sensor but both voltages check within
>specs. I'm not getting any error codes and the car drives great at all
>other times. Any ideas? Thanks.

It seems like you do not have a clean switchover from close loop mode or worn TPS around 1/8 throttle position. Is it the same when you do quick WOT?

I would start troubleshooting by measuring the TPS linearity across the range. Probably the resistor / wiper arm contact is worn around 1/8 throttle. When driving normally in average street traffic you are mostly operating around this range. Only when you notice Rustang or Slomaro then you start using full TPS range ;-)

I would take a voltmeter and plot TSP resistance over the full range. The factory test checks only 2 points. If you find some unusual reading around 1/8 throttle, do not be surprised.... Just replace TSP.

If the readings seem linear enough, then I would buy good electrical contact cleaner / oxidation remover (Like Wurth Contact OL) and spray the connectors. This usually takes care of any intermittent readings of TSP.

Old plugs also would give you a slight stumble when transitioning from deceleration to acceleration but you would not have seen the drop in fuel delivery. It seems like CPU is being delayed in making a decission during a transition between open loop and close loop. This points mostly to electrical problem or bad sensor.

Make sure that your battery terminals are clean and you have good grounds before you start troubleshooting. Establisiong that CPU is referenced correctly and really sees the same values of sensor outputs is critical.


Date: Sat, 23 May 1998 11:54:10 -0400
From: (Chris Sychlovy)

I would begin by unplugging the O2 sensor to force the ECU into open loop operation. It's very easy to do and should tell you conclusively if the problem is caused by the closed loop to open loop transition (as I suspect it is) or some other problem. The O2 sensor connector is located between the extension maniflod and the firewall.


> The car starts and idles perfect but after about four or five minutes the
> idle will fluctuate between 1000 and 1500 rpm's, if you give the car light
> throttle it will climb all the way to redline fine, but if you give it a
> quick deep throttle blip the car chokes and gasps and you cannot drive it
> because  under any load it will make no power!! 
> Here is what i have tried: at the ecu i have checked  the voltages of the
> TPS sensor,map sensor,intake sensor, idle air control all of them
> check ok, i have swapped ecu's and it still does not make a difference!!
> it seems like the car is leaning out to the point that it will not run, even
> with the intercooler pipes removed it still does it which means the turbo's
> have nothing to do with it! 
> The car is a third gen with exhaust ported motor stock sequential
> turbo's, stock ecu(for now) and stock ignition (for now), the motor is new and
> nothing electrical has been added to the car.  

From: Ryan Schlagheck (
Sent: Friday, January 21, 2000 10:33 AM

I've taken the car to KD Rotary three times to have this looked at, in addition to other maintenance. We have been through everything on the car, just short of flowing the primary and secondary injectors and fuel pump.

I could write reams and reams on what I have done myself, and what Dave Barninger at KD Rotary, Brian Richards at M@ Performance, Ray Lochhead at Shane Racing, Roger Mandeville at Mandeville Auto Tech, Trey Cobb and Ari Yallon at Rotary Performance, and some mechanic (not Cam Worth) at Pettit Racing have said were the _possible_ causes, and none of the recommendations proved to fix the problem. Note that the above persons, with the exception of Dave at KD Rotary were diagnosing over the phone. This is not an attack on their knowledge of the rotary - no flames over this please. Just trying to get my car healthy again.

Once again, I would like to poll the list-at-large for any suggestions. Here are the things I've checked:

My vacuum at idle is 500mm/hg, pretty healthy. I can build boost all the way to 14psi. If I part throttle the car in any gear, I can climb all the way to redline smoothly. If I go WOT in any gear, I do a bumblin', tumblin', stumblin' run to redline - that is to say, it's not smooth at all.


From: Steve Obrien (
Sent: Friday, January 21, 2000 1:25 PM

My friends and I have worked on about 7 FD's and one of my friends had a somewhat similar problem to you Ryan. We tried everything just like you but it came to a point that we figured that the main wiring harness has need fried somewhere in the system. Massed puts a really crape wiring harness in the FD's, for a car that generates so much heat as a rotary I think they could of used a better quality harnesses and lines. Well to make a long story short we ordered all of the necessary wires and harnesses from MazdaComp and we rewired the entire car again and the car was fine after this.


Date: Fri, 21 Jan 2000 13:30:24 -0500
From: "Ryan Schlagheck" (

Hmmm. New harness. That's what I'm afraid of. Ray Lochhead also mentioned putting these into two different cars when all else failed. Everything was fine after that.


Also see the page on 3,000 RPM Hesitation Troubleshooting. --Steve

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