87 5.0 low speed surging/bucking?

my 87 mustang gt started surging at low speeds. egr is blocked off, fuel pressure good, new plugs, wires, dist cap, rotor. I'm thinking flat spot on tps. Suggestions?


It is mass air converted. Full exhaust: BBK headers, off road x, magnaflow catback. It does have a cold air intake. Cleaned mass air sensor. Can't find an air leak. Fuel pump changed about 10 years ago. I've had the car since 95, it sits alot, I've only put 25000 kms on it since 95. WOT no problem, light throttle surging.

Update 2:

When I blocked off the EGR I used a homemade plate. The sensor is still hooked up.

3 Answers

  • 10 years ago
    Favorite Answer

    Did you block off the EGR using the kit from RJM Technologies? It consists of the plate and a sensor eliminator. You can't just simply block it off and leave the plug to the EGR hanging loose if that's your case. That's going to be part of if not the actual problem. Yes, 1987 is speed density, but NO there isn't a meter in the intake tract. Mass air meters didn't come in Mustangs until 1989 (1988 in California). You also didn't mention if your car has had an upgrade to mass air already, Shawn. Fan wash is a misconception. A mass air meter will not cause the engine to surge from fan wash. The air being sucked into the intake tract is traveling faster than the air pushed back by the fan. You also didn't mention if you still have the stock fan or an electric fan kit installed. For future reference you need to list ALL mods made to the car in order to help with getting a more precise answer. Below is the link to the EGR Eliminator. Also, if you try adjusting the TPS (which you shouldn't be anyway unless it's actually bad; those go bad eventually now since they are old) you need to keep the voltage between .95 to.98. Do not mess with the adjustment screw under the throttle body being that your problem is a stumble, not the idle.

    Source(s): http://rjminjectiontech.com/products/egr-eliminato... forums.corral.net/forums
  • 10 years ago

    Helmut s correct about your blocked off EGR. Off topic, these cars will also "Buck" at low RPM , as they're hunting for torque. One very cost effective addition for you is to buy a set of Pedestal Rocker Arm Shims. They're CHEAP..! They'll put power in the engine for you from idle and throughout, and you will gain mileage, as well as clean up the idle quality. Keeping a warm Thermostat in them also helps these things.

    FYI: Those cars make more power everywhere with small exhaust than big exhaust. 2 1/2 is way out in left field for them, both mileage & power will suffer.

    Email: camshaftshaun@gmail.com

    Source(s): Camshaft designer/manufacturer, full competition race engine builder, carb blueprinting, internal engine component failure analysis.
  • 10 years ago

    Intake air leak maybe

    I'd say faulty fuel pump, but if the pressure's good, don't start there.

    maybe a loose fuel injector wire harness connection

    Lastly, check for a defective PCM or information sensor.

    Source(s): haynes repair manual: troubleshooting "Engine surges while holding accelerator steady"
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