1996 Geo tracker, 1.6 litre 16 valve. 4x4 auto ac (not charged) power steering.

I have a tracker that I just installed a new rebuilt engine in. it has a shimmy/ misfire at idle. the car has about the right amount of power you would expect for a 90ish hp engine. revs well. absolutely no trouble codes or DTC. car is a tad hard to start but does so. idles right up to about 1800 for 10-15 seconds, falls to 1200, and then at temp it falls to 800-850 range. that is when it develops an intermitant miss. the car has idled about 2 hours after install to attempt to hunt the problems usually about 10 or so minutes at a time. the block and head were both done at a local machine shop. all new valves were installed, piston bored to .20 over. the engine has: new oil pump, new head gasket and bolts, new timing components, belt, tensioner, crank cog. (timing is perfect on the two marks, new mass airflow sensor, new ISC (Idle air control vavle) and new fuel pressure regulator. new plug wires and plugs and cap.

I have checked for vacuum leaks with the water bottle and found nothing. I have done a compression test and all cylinders show 150 lbs evenly across all cylinders. (rings have not seated) valve lash is correct at .007 cold. timing is set with the jumper pin at 5degrees before TDC. I have pulled spark plugs and gone to ground and the motor slugs and then recovers when they are re installed. TPS is set with an ohm meter it reads 0.00% also on my scan tool until you ever so slightly touch the throttle and it then reads. I have only used the long screw driver on the injector and can hear a click on every one of them that sounds similar. If I unplug the MAF the engine dies, If I use a vacuum hand pump on the EGR the engine stumbles and if I hold it the engine dies. If I unplug the ISC(IAC) the engine slows to about 400 rpm and stumbles horrible. it did sit 2 years while I was waiting on another block as the original had a crack in the journal between 2-3. I made a mistake of thinking it would be quicker and I did not drain the fuel. I have since ran it empty and added some premium . but the problem still exist. I have a basic blue tooth scanner, and an ohm meter and willing to rent or buy any other tool to get this running correct. thanks in advance for reading this and helping.

Tps needs to be checked in volts dc on signal wire should read between .5 and 4.5 volts. Have someone press slowly down on gas pedal (key on engine off) till at floor and slowly release while watching meter. If at any time it reads 0 volts it is bad. With a ohm reading of 0 i think it is bad as it is a variable resister circuit.

Ok I retested. the unit has 5 volts on the grey and red wire.
pin 3 to ground shows .4 volts and when throttle is opened it goes to 4.5 volts.

I also set the tps by the service manual with .026 feeler gauge between the stop plate and the idle set screw. and adjusted till the tps has continuity, then tightened it down snug and removed the feeler guage. the test then showed open. so just the slightest blip of the throttle shows continuity.


I restarted and the dtc showed the tps where I had unplugged it with power but other than that no other codes. the engine still idles rough. it also has a slight bog at acceleration.

I am curious if this makes any sense I feel like an injector has some jelled varnish from old gas in it and leaking. I have another set of injectors that I got off of ebay (from a wrecked 98, factory ) it really is not much work to change them, could this be the issue?

Did the tps signal go from .5 to 4.5 volts or just stay at 5

If it stayed at 5 its bad

no sir It evenly moved .4 all the way up to 4.5 at full throttle half throttle was like 2.7

Do you have a fuel injector tester and fuel pressure gauge? If you do you can pressure drop test the injectors. And see if each drops the same psi.

I have a fp guage but no injector tester. I will purchase one on amazon today. thank you for your help I will post here when I have results.

Ok with the fuel pressure tester you will need to find the fuel pressure test port on the fuel rail if equiped. And attach the tester to it. Then turn key to on position (engine off) and read the pressure. Does it hold pressure? What is the reading? Most fuel injected systems operate between 40-60 psi when engine is off. If it holds pressure in that range and does not drop over a ten minute period its safe to say your injectors are not stuck open/leaking.

If it is not holding pressure in that range you will need to block off the return line if it has one and cycle key off and back on and get a reading. if it holds pressure then your fuel pressure regulator is leaking.

If its not then remove fuel rail and rest injectors on top of the ports making sure injectors have a clip holding them to fuel rail if no clip holding them on stop you will need to makeshift a way to hold them in with zip ties or something first. After securing injectors then cycle key on and observe the injectors for spray. if none found and pressure still drops proceed to next step.

If it still drops then remove fuel feed line from rail and attach fuel pressure tester to it and cycle key back on and read pressure. Does it hold pressure for the ten minutes or drop? if it drops its the pump or fuel line leaking. Check fuel line all the way back to tank. If no leaks found (wet spots) then fuel pump needs replaced.

Ok guys I got my scanner all ready today and started working. I got to here, timing is close it starts a lot better, but I am stuck in open loop due to insuffucuent engine temps. I will check' for a stuck thermostat or bad sensor. I will report my findings. thank yall for your assistance!

my sensor tested bad. I picked one up at Oreally and it went into closed loop. fuel is trimming about 13% at idle and no other codes. best news is that the rough idle seems like it is corrected, thanks so much for pushing me in the right direction and being patient with me

Which sensor did you replace?

the ECT sensor was not moving from 200 ohm. in the freezer it read 200 ohm and in the boiling pot it read 200 ohm. guess it was enough not to freak out the computer but not enough to put it into closed loop. I replaced it and now when the engine is just getting to the 180 degree of the thermostat the engine will go into closed loop and the idle smooths out, I have not driven it because the seats are at the upholstery shop but I would guess long term will record after a while and correct the long term fuel trim and start up.

That would do it. for some reason ect and iat sensors when the stay stagnant it doesnt flag a code. You would figure someone would have thought to write a program for the ecu to compare coolant, intake air and ambient temp to determine if a sensor is stuck after 20 minutes of run time. But maybe they will get to it at some point.

Lots of vehicles would've popped a P0128 for the ECT stuck cold. I guess the OPs Tracker being 1st year of OBD-II it doesn't have that functionality.

And apparently FCA do compare AAT, ECT and IAT on a cold start.

www.dtcdecode.com/Dodge/P1115

Thanks matt that is good news less headaches for us all