Idle Drop/Surge at idle.

1990 4l auto. Idle drops every 20 seconds or so. Happens in Park or in gear. However when in gear it feels like its going to stall out but never does.

Heater in the off position (thought of AC kicking on)
Tried multiple tps's but now has Newer tps adjusted to .83
Tried multiple IAC's cleaned all of them Happens even with the iac disconnected

Ford 19lb injectors
seafoamed
newer plugs, cap, rotor, fuel filter
reset ecu
no vacuum leaks that i can find

Thinking maybe either EGR cleaning or o2 sensor??


http://www.youtube.com/watch?feature=player_profilepage&v=haVT1BBn2LA

Get out a can of throttle body cleaner and start spraying around anywhere there COULD be a vacuum leak. With the engine cold, snug up your intake bolts. Do that anyway as preventative maintenance.

You can open and close the EGR with the engine running by pulling the diaphragm back with a coupla fingers.

If it's okay cold and then has a crappy idle warm, it could be your oxygen sensor.

Thanks I will check those things. Any other ideas anyone?

i am having this same problem and going through it right now.
i am considering jumping the ground straight to the body from the TPS to rule the grounds out.

I would start with renewing all of the grounds.

Your idle is absolutely dependent on the IAC, and the IAC is nothing but a stepper motor that extends/retracts upon commands from the ECU. The ECU determines what it wants the IAC to do based on data from a bunch of sensors--CTS, crank sensor, synch sensor, TPS, MAT, MAP.

Do the grounds, then TEST your sensors.

IACs rarely fail, but they will become lazy and respond poorly to commands--sit, roll over, beg, extend, retract, etc.

joe_peters said:

I would start with renewing all of the grounds.

Your idle is absolutely dependent on the IAC, and the IAC is nothing but a stepper motor that extends/retracts upon commands from the ECU. The ECU determines what it wants the IAC to do based on data from a bunch of sensors--CTS, crank sensor, synch sensor, TPS, MAT, MAP.

Do the grounds, then TEST your sensors.

IACs rarely fail, but they will become lazy and respond poorly to commands--sit, roll over, beg, extend, retract, etc.

Click to expand...

Dumb question but is there a schematic online or can you tell me how many grounds there and were they are located. Obviously i know of the battery and head to firewall. Are there more?

Credits go to kastein for posting this in response to my question a few days ago.

Grounds on the XJ:
* from the firewall to the back driver side of the head (self-destructing braid, as Matthew noted.)
* from the negative battery terminal to the inner fender wall
* from negative battery terminal to the block, just below the coil (as noted. This is where it was on my 96 from the factory.)
* from wiring harness to dipstick mount stud (these are for sensors, ECU, switches, etc. Rather important if you want the engine to run right)
* from the wiring harness to the fender wall, driver side, near the ECU - for a bunch of the HVAC system, dashboard, ECU, transmission control (wtf? no idea why the HVAC/dashboard/TCU stuff is grounded to here, blame Chrysler) this one LOVES to come undone if you have large tires and minimal bumpstopping and bash on it a bit, because your tire will smack the tip of the screw repeatedly till it strips the hole out. Don't ask me how I know
* possibly one somewhere under the dash. Haven't verified this.
* one inside each rear fender in the cargo area for the lights and some other stuff.
* on the MJ, the ground behind one of the taillights also runs the fuel pump. Yeah, WTF?

Ok. Pulled,cleaned and checked the grounds: passenger fender, dipstick tube, battery to block, firewall to intake manifold, drivers side fender ground was super loose. I don't have one that runs from battery to chassis.


Didn't fix the problem but the thing starts like a bat out of Hell.

Also found out it only happens the first 2-3 minutes after its started. Happens 4 times then idle smooths out. Doesn't matter if cold it warm or how long it sits. I just confirmed this like 6 times..

Tapatalk - Droid Incredible

Also I removed and cleaned egr with new gasket etc.

Tapatalk - Droid Incredible

Tightened all intake bolts.

If its doing it when its cold its safe to rule out the o2 sensor. They don't come into play until the engine is warmed up to operating temp.

b16a90teg said:

Also I removed and cleaned egr with new gasket etc.

Tapatalk - Droid Incredible

Click to expand...

did you function test the EGR solenoid and it's associated vacuum nonsense?

I don't have the FSM here in front of me, but there is a procedure to test it. Either that or unplug the vacuum harness to the EGR solenoid and plug it. his will disable the EGR, good for troublshooting.

whats your input/output voltage the tps?
my thread on here is trying to diasnose a very similiar problem.

4.69 input 3.92 out. Some say .83 others say 4.15 out. And all data says .85 so I figured .83 or .85

I will double check when o get home but I can't remember if it happens after fresh cold start or just after restart. And ill check egr with a vacuum tester. But when I removed vacuum line I have vacuum going to it but nothing changes.

youre lucky,
right now im getting 9.7 in, 8.1 out.
something is up...
im at .83 ratio, but with way too high of a input voltage.
not sure, but ill start checking continuity next

did you read up on how to test the EGR valve, transducer, and solenoid?
its more than removing the vacuum line...
i busted out the mittyvac last night and went to town.
all of that egr stuff is good on mine...

also hit all my grounds.

tonight im gonna warranty the TPS, and wire the ground for the TPS to the firewall.

TESTING
EGR VALVE
Valve Opening Test

• With engine at normal operating temperature and at idle,
  rapidly open and close throttle. Open throttle sufficiently to obtain
  at least 1500 RPM. Movement should be noticed in EGR diaphragm.
• If diaphragm does not move, probable causes are: faulty
  vacuum signal to EGR, defective EGR diaphragm or defective
  backpressure sensor diaphragm (if equipped), or leaks in vacuum lines
  or connections.

Mine doesn't move when giving it throttle. Hmm still digging threw the possibilities.

The EGR on my 90 is different then others I have seen. It doesn't have plate that I can reach in and move with my fingers. It seems to be all sealed, all there is is a rod going through the middle. Only way to move it is a flat head screwdriver against the shaft.

Also it does do it cold or warm but worse(more noticeable) when warm.

Remove the TPS connector from the TPS--remove the 4-wire connector if auto equipped. Key ON, measure "A" positive to "D" negative--note the voltage, that is your "reference" voltage. Put the connector back on the TPS. Back probe the connector at "B" positive and "D" ground (use small paper clips with straightened legs). Key ON measure the voltage and adjust that voltage to 83 percent of "reference" voltage for auto equipped XJs and 17 percent of "reference" voltage for manual trans XJs. If you can't achieve the correct value replace the TPS and try again.

I have long probes on my multimeter so no need for paper clips(I dont think)

The only thing I didnt do in your procedure is unplug the TPS to check "reference". I checked it while plugged in. I will try testing "reference" while unplugged.

BTW following AllData Pro procedure I have it tuned to .83 (4.69 in 3.90 out) 3.90/4.69= .83155650

Bout as close to .83 I could get it. lol.