RDS928S

1986 928S
sporadic exhaust popping and engine miss and or buck at idle only.
Getting worse as time goes on.
Items that have been replaced:Intake R&R, Idle speed control valve,Temp II sensor,Complete tune up, o2 sensor etc.
The only variable is the Throttle position switch which was bypassed when it crumbled in my hand.

Thanks Rich

Bill Ball

What do you mean by the statement that you "bypassed' the throttle switch?

Mrmerlin

Does a full tune up mean you added a new set distributor caps and rotors and wire set? Start the engine and Spray some water on the wires after dark look for the wires snapping and blue sparks jumping, I think you need to fit a new TPS as well and check the other parts that were under the intake, both knock sensors should have been replaced as well as the TPS, the crank position sensor, and the flappy vacuum pot, also the hall sensor should have been replaced, also check the coil grounds if any of these wires are corroded they should be replaced, check the vacuum dampers, and fuel pressure regulator for fuel leaking into the vacuum lines, check the O2 sensor connections.

928ntslow

Sounds like the car is "hunting". I think you answered you own question as Bill points out. I would be suspect of vacuum if that doesn't cure it.

JHowell37

'86 doesn't have a hall sensor, flappy, or knock sensors. I too am curious as to what it means to bypass the TPS.

RDS928S

The TPS plastic case crumbled during the intake R&R.
The three wires were connected directly to one another.
Tune up did include new wires,dist. cap,rotors,plugs and coils.
New adjustablef uelpressure reg. was also installed.

Bill where is the hall sensor?
The strange part is this problem comes and goes. Most times the car runs great.

Thanks Rich

Mrmerlin

OOpps sorry I misread the year, no hall sensor or knock sensors, Thanks Jhowell37.
I would check the TPS wire bundle, and the coil wire grounds, also check the connections to your brains and take a look into you CE panel for water dripping signs pull all of the fuses to see if there is any corrosion if so you need to reseal the bottom of the blower box also check the hot post connections under the hood and open up the 14 pin connector looking for corrosion, check the coil wires to the caps and the coils

RDS928S

Some pics of the three wires tapped together for the TPS.
Anyone use Carl's new three wire connectors?

Thanks Rich

John Speake

Did you refurb the injectors ?

RDS928S

Hi John,

no-injectors are original.

The problem only rears it's ugly head every few weeks and at idle only.
Once off idle the car runs great.
Another possible related issue is sporadic hard starts.

Thanks Rich

John Speake

I had a misfire on my Euro which turned out to be a bad injector. It was intermittant also.

I had a set ultrasonically cleaned, and fittd them - problem solved.

Have you set the idle CO to 1% as per the Workshop manual ?

RDS928S

John,
good tip. Will do with the injectors and CO%.
Did your car also suffer from hard starts?

Regards Rich

Mrmerlin

you might be better off repacing all of your injectors with the new 4 hole type the price is hard to beat, We just rebuilt Matts intake 2 weeks ago and the new injectors work great with awesome throttle response, I think the TPS also needs a new connector new set of injectors 279.00

RDS928S

Mm,

ok will order the injectors from Dave. Does the intake need to come off to replace them?

Rich

PorKen

I'm guessing the idle switch connection is intermittent.

Check the ignition timing at idle. It should be 10° (13° cold). If the idle switch is disconnected or broken, it will be 20° (23° cold), which will make it more difficult to start, and the idle will occasionally stumble and drop out. Also, with an auto, the idle correction will be 'aggressive'.