87 S-10 intermittent starting/running issues

Power/Fuel
1

I have a 1987 S10 with 52000 miles. It has the 2.5L “tech 4” motor with the throttle body injection and 4 spd auto transmission. I am the second owner. My grand bought in new, then drove it for a few years. Then it sat in the barn being driven once or twice a year.

It has good days and bad days.

On the good days the only complaints that I have are

  1. Hard to start when cold - the motor turns over just fine, but does not fire. Below 30F I have to pour some fuel down the throttle body to get it started. Below 20F I just gotta wait for warmer weather. On a good day in warm weather she starts just fine.
  2. Hard to start when hot - run at highway speed for 1hr + in the summer and it will not start until it cools off.
  3. Disappointing fuel economy. I was expecting mid 20’s MPG on my mostly (55mph) highway commute. Instead I am getting around 18 MPG.

On the bad days add in

  1. Gotta pour fuel down the throttle body to start no matter what the temperature.
  2. When engine warms is warm at highway speed it pings/knocks on light acceleration or going up a modest hill.
  3. Sputters and tries to stall with throttle in middle of range. If I back off to idle or floor it it starts to run again.

The bad day symptoms go together and keep happening until I drive it for 1hr plus or shut it down for the night. I get about one bad day per week.

When I first started driving it at 48k miles I took it to a mechanic I trust to give it a complete tune up / 50k maintenance. This includes plugs, wires, dist. cap (points if it has 'em - don’t remember) fuel filter and air filter. This tune up improved the highway MPG from 14 to 18 but did not help the other issues.

Problem is that I never managed get it to a mechanic on a bad day. I am looking for anything that I can do to help diagnose or localize the intermittent bad day problems.

2

Find a garage that has the equipment to work on cars of this era. Too many places have become reliant on trouble codes to repair cars. I would suspect a failing coolant temperature sensor, a faulty fuel injector, sticking EGR valve, or a fuel supply problem.

3

Do you have the ability to dig into this yourself to some extent?
You could jump the A and B terminals on the diagnostic connector to see if it spits out any codes.

The pinging usually points to an EGR system fault; likely clogged passages or a stuck pintle. Pinging can also be caused by too much timing advance if someone has dinked around with the distributor and not grounded the ESC connector during a timing check. My assumption is the distributor is correct.

Due to some unknowns I feel like any comments I make about the starting issue would be wild guessing at best although I tend to also think the coolant temp sensor or fuel pressure could be an issue. Maybe the residual fuel pressure is bleeding off while the engine is at rest.