Got a puzzler that I know someone has had the misfortune to resolve in recent history! Newly rebuilt 2.0 4 banger, with virtually everything new; ran great until it started showing signs of extreme rich fuel mixture. Traced that back to a misplumbed fuel pump (imagine THAT ever happening!) which doubled the fuel pressure and consequently increased the amount of fuel delivered! That issue is now resolved, but now, when the car comes to a stop, the idle drops to just above "0" and tries to quit, but usually catches itself and then goes up to about 900 rpm, and is fine... Not critical but very irritating in an otherwise super strong running 2.0.

Guesses... Throttle Position Sensor? If so how to fix, or just find a replacement?
Vacuum leak? Have all new lines and will be tackling that project this winter. Other ideas? Open to all suggestions... hate to just start throwing parts at it since many are not even available any more!

Thanks in advance, Gang!

FI or Carbed?

If it is FI I would check the CHT gauge! Does it run better when cold?

Jeff

100% original and stock Fuel Injection... Brand new Cylinder Head Temp Sender; less than 100 miles on it!

Some other components are new... some are original...

But, yes it does seem to run better at first and then the idle gets "irritable" after completely warmed up....

Cold Start Valve is not functioning at the moment... just for info...

my fresh 2.0 did the same after about 200-300 miles. just a simple adjutment on the idle screw, and everything was peachy. i have not had to adjust it since. mine also does not have thermostat (if it matters)

....bad injector....leaky, running rich at idle causing it to stumble.
Under load, it would or could run strong.

Could be running rich at idle. Try adjusting the idle mixture screw on the ecu. One direction makes it rich. The other lean. Never can remember which is which. I "think" full clockwise is full rich.

Did you have a chance to seat the rings?

Curt

turn "R"ight = "R"ich
turn "L"eft = "L"ean

Did you check the CHT and the intake are temp sensor check pbanders site: http://members.rennlist.com/pbanders/DJetParts.htm for details on testing. I was able to diagnose a similar problem with my CHT using his site.

Also how is your wiring harness (futz with the connectors and see if the engine runs differently)? I also replaced mine with a rebuilt one from Jeff http://members.rennlist.com/914_wiring_harnesses/

Dan

I put a new CHT in and had the same problem. It turned out to have stripped threads and would not give an accurate reading.

Jeff

Make sure timing, dwell is spot on. With points it takes a while to get it perfect.

That seemed to make a difference for me when I had issues like that.

Some random thoughts:

Check the spark plugs and make sure they aren't fouled from running rich.

Depending on how the fuel pump was plumbed, it might have been sucking gas in from the return port of the tank, and in doing so sucked in a ton of rust and other crap at the bottom of the tank. This gunk might be clogging the fuel injectors and causing a misfire on one or two cylinders at idle giving you the poor idle.

Once it recovers from the low idle and goes back up to 900, how does the idle sound and feel? Is it perfect or still lumpy? Will it keep idling at 900 indefinitely?

It could also be that you dont have the decel valve plumbed correctly.

I would probably start with the basics - make sure everything is hooked up correctly, then go thru the ignition system, points, timing, etc. Then adjust the valves, etc. You are bound to find it eventually.

You know, the plugs COULD be fouled AGAIN! Did not check them after the pump got replumbed, and YES, it could have sucked up all the crap from the floor of the tank! Soooo.... Guess it wouldn't hurt to have the injectors cleaned and tested, even tho they were new a few hundred miles ago! The idea of checking the ECU setting is probably valid also; had not done that; as far as I know, it is the original factory setting, BUT.. after 34 years, no guarantees there!!!
After idle stabilizes, it seems fine at around 850 to 950 rpm... not always completely stable, but in that range...
Timing and dwell have been checked by a very qualified mechanic (not me!) and all seemed well there, so back to the fuel delivery system...
The car runs especially strong once "Off Idle" In fact, this is the best running factory injected 2.0 I have ever driven or seen, for that matter! Which could indicate it is set way too rich at the idle end of the spectrum??? It actually "feels" stronger than a very solid 2.0 factory six that I owned a few years back; yes, subjective, but... tons of low end Grunt and pulls all the way past redline in every gear! So... play with the idle adjustments and check the plugs and see what happens...
Thanks to all of you for the ideas... if we find anything really indicative of the issue, I will post it! Enjoy the Holidays!!!