I need some ideas for my 86 EA82T wagon with double core radiator, consistent bogging at low temperatures and after even slightly letting off on the gas.  It feels like the plugs are fouling from too much gas.  I have changed out distributors.  I have checked and rechecked the timing.  I have put new plugs in it. I replaced the coolant temperature sensor.  When the outside temperature are higher, the better it runs.  The longer I warm it up in the morning, the better it runs.  With outside temperatures in the 30's and little warm up, it starts bogging pretty quickly.  It does not seem to burn either oil or coolant to any significant degree.  I need some more ideas for things that I can replace.

Smooth cold idle?

Healthy spark?

Checked plugwire resistance?

 

I would check fuel pressure.Maybe your pump does not like the cold or is just weak.

Poor cold starts were the first symptom of a weak pump on mine.

Car ran amazingly well otherwise,even under boost!

 

Seems unlikely.but a bad air temperature sensor in the MAF is possible.

Not much service info available.I would compare sensor resistance to another or sub a known good MAF for testing.

 

Coolant temperature sensor might still be wonky.

I would check its resistance.

Double checking CTS resistance at the ECU plug might help.

 

Unmetered air or vacuum leak that seals w/rising temps is another possibility.

The rubber intake tract and PCV hoses are among the suspects.

86 - so it is flapper afm style ? with the cold start air bypass mounted on the coolant thermostat housing?

I should also say that it could be more related to humidity.  As air cools in the evening, the humidity goes up, and the bogging begins.  When it is raining, it will bog while cruising along at a constant speed, no matter what the temperature.  I replaced the pcv valve with a new one.  I also replaced the fuel filter.

 

It idles smoothly on a cold start.  It appears to have normal power for climbing hills.  I currently have about 1/3 or the radiator covered in order to keep engine temps up.  When it bogs, I can rev it up to clear it out.  Then it runs normal for a little bit.

That makes it sound more like leaky insulation on the plug/coil wires,cracked cap or very dirty coil top

If you get a light show after misting the wires w/water at night,you can be sure.

Edited January 6, 201412 yr by naru

Fuel icing perhaps,  check flapper unit and associated vacuum pipes on intake to aircleaner housing if it has this and  a bypass pipe? that draws warm air off  exhaust manifold? if it has this also?

Not sure how turbos / fuel injected are set up but this is how N/A carburettor engines are.

Edited January 7, 201412 yr by subnz

I sprayed a mist on the electrical components when the engine was running and it had no effect.  The car is fuel injected MPFI and turbo charged.  The bog happens instantaneously as soon as you stop accelerating.  This occurs during cold temperatures in the 30's and in heavy traffic with water spray flying from rain storm, at any temperature below say 60 deg F.  All the plug wire contacts are free of green corrosion.  The engine has full power when not bogged up.  Nothing unusual coming from the exhaust.

Absence of a light show after misting the plug wires does not mean the insulation is good,

You might try misting them again and running your hand along them w/engine running.

You will know when you find a bad one.

 

Measure plugwire resistance too.

Absence of a light show after misting the plug wires does not mean the insulation is good,

You might try misting them again and running your hand along them w/engine running.

You will know when you find a bad one.

 

Measure plugwire resistance too.

Agree spark plug High tension leads / ignition coils can do strange intermittant things when failing sometimes (ie break down under load)  may not see a visible fault / short.

Edited January 9, 201412 yr by subnz

I have concluded that the problem is caused by the coolant temperature dropping below some minimum that the computer needs to keep things running smoothly.  Driving in a rainstorm provides an even more rapid heat loss through the radiator, so that the engine is not making heat as fast as the radiator is losing it.

Problem solved.  I bought a new coolant temperature sensor that screws into the back of the radiator.  No more bogging.

Problem was not solved.  A new alternator did solve most of the remaining bogging.