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Old 12-13-2018, 03:18 PM
mrbieler mrbieler is offline
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My son is driving our 1997 D1 4.0 GEMS truck right now to school. The other day it started to sputter and stall at idle and hiccup at RPM on the way home. Thankfully he safely limped home.

I couldn't detect a vacuum leak. Removed and cleaned the ICV and MAF. Battery and alternator check OK.

Fires right up and usually idles at the appropriate range, but after a bit the idle drops to below 500. If you push down on the gas hard, it will dip, but recover, but if you're light with your foot it stalls.

If I hold the RPM at 1000 or 2000, it will briefly hold, but after a minute or so will sputter, surge and drop. If you let off gas it will drop to about 400RPM and stalls about 1/2 the time.

No CEL and no OBD II codes popping up.

I need some direction here.
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Old 12-13-2018, 03:25 PM
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WaltNYC WaltNYC is offline
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The IACV is notoriously sensitive. I've read many times that you should NOT change the position of the pintle while cleaning it. There are reports that the ECU (engine mgt computer) will need a re-flash.

I was experiencing similar symptoms. I replaced my IACV with a unit from Napa auto parts (# CRB 21856... from a 4.0 L Jeep) for about $55 (get a new gasket too) rather than the genuine LR part which will run you $175. Again, some have reported that upon replacement their truck would not idle properly until the ECU was re-flashed. I was fortunate in that all I did was pull the pintle on the new unit to approximately the same position as the old unit, installed it, and was good to go.

Since that time robertf has developed a re-flash tool so you should be covered in that case as well.
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Old 12-13-2018, 07:17 PM
mrbieler mrbieler is offline
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I did not mess with the plunger. In theory, it’s a servo and should correct it’s position when you install/reinstall it.

After driving it around, it seemed to adapt and ran great. Stop and go streets and a quick freeway run. I shut it down and waited a few hours. Acting up again. All the same issues are back.

I might go buy a new icv. Local ORiellys has one in stock. $50.
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Old 12-13-2018, 07:28 PM
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How's your fuel pressure? I was having similar symptoms with low idle a couple weeks ago when my pump was going bad.
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Old 12-13-2018, 07:59 PM
mrbieler mrbieler is offline
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I can look at the fuel pressure, but it was running great once it gets going. there’s no issues at RPM under load. Only issue is at idle and on acceleration from idle.
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Old 12-13-2018, 08:31 PM
mrbieler mrbieler is offline
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Just got home and took it for another spin. Even worse now. It outright cuts out at a stop or it will race and hold 2000rpm. ugh.
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Last edited by mrbieler; 12-13-2018 at 08:49 PM.
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Old 12-14-2018, 10:08 PM
mrbieler mrbieler is offline
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Well things took a turn for the worse today. New ICV valve installed and now it's running very rich. Starts up easy and idle goes to about 700 or so, but soon falls off and stalls. The idle jumping to 2000RPM and holding is gone.

After starting, when I get the RPM up to about 1500~2000, it begins sputtering. While running, I unplug the MAF. No change in performance. No engine codes at any point over the last 2 days.
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Old 12-15-2018, 12:26 PM
mrbieler mrbieler is offline
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I think I've ruled out a fuel system issue.

Pump making the usual noises and fuel pressure measured:

38psi at position 2/accessories
34psi immediate ignition off
28psi at 20 minutes
26psi at 40 minutes
30psi at idle
29psi at steady 2k rpm
30~34psi blipping throttle
34psi at immediate engine off

Area around the injectors is clean and clear of any signs of rust/leakage/etc.

Idle still wanders. Holds high at about 2000 if left alone. Drops below 500 if I hit the gas. Wanders +/- 200rpm and then stalls.

Still not showing any codes on my scanner.
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Old 12-16-2018, 03:25 PM
mrbieler mrbieler is offline
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Well I think I'm in trouble.

Did a cold cylinder test this morning. 2,4,6,and 8 were all about 120psi. 1,3,5,and 7 were all 130~140psi

On restart, I'm running very rough. White smoke from exhaust and water. Decent sized water stain under the muffler.

New head gaskets on a 22 year old salavage title truck with 150k miles on it? Maybe time to walk away.

Still no CEL and nothing on my OBD scanner.
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Old 12-17-2018, 07:25 PM
_ExpeditionMan _ExpeditionMan is offline
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Following along with you Jeff. Have similar symptoms with my truck without the wandering idle. No issues with overheating or fuel pressure either.
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  #11  
Old 12-18-2018, 12:13 AM
XCELLER8 XCELLER8 is offline
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your cylinder pressures are not "terrible" for a vehicle with that mileage , a few questions for you...
1. has the engine overheated recently ?
2. are you losing coolant ?
3. does your truck have "AEL" ?? advanced evaporative loss emission system ?? it will say on the emission decal under the hood, also the
AEL models have a rectangular charcoal canister (non ael's have a round one).
let us know ...the AEL models have a few more quirks....and it fits your symptoms
my '98 acted the exact same way and it ended up being a faulty fuel tank pressure sensor
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Old 12-18-2018, 10:30 AM
mrbieler mrbieler is offline
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no issue with engine temps. only time was 5 years ago when the fan clutch died.
minor coolant loss has always been an issue. every 2 to 3 months I add about 1/4" of coolant to the evap tank to cover the post. i believe it's a slight weep at the rear of the engine.
It has AEL

Strong smell of gas at exhaust and now some in the evap tank. Plugs are sooty and dry. Obviously running very rich. Still puzzled by the lack of codes or CEL.
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Old 12-18-2018, 03:50 PM
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Did you actually check for any codes, or are you waiting for the check engine light to come on?


Do You see a check engine light when you you turn it over ?
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Old 12-18-2018, 05:26 PM
mrbieler mrbieler is offline
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CEL comes on at start as normal and then goes off as normal. The bulb works. I have hooked up an OBD II scanner and it's showing nothing.
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Old 12-19-2018, 12:43 AM
XCELLER8 XCELLER8 is offline
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Quote:
Originally Posted by mrbieler View Post
no issue with engine temps. only time was 5 years ago when the fan clutch died.
minor coolant loss has always been an issue. every 2 to 3 months I add about 1/4" of coolant to the evap tank to cover the post. i believe it's a slight weep at the rear of the engine.
It has AEL

Strong smell of gas at exhaust and now some in the evap tank. Plugs are sooty and dry. Obviously running very rich. Still puzzled by the lack of codes or CEL.
ok....try this >>>...access the fuel pump under the rear carpet ( just roll up the carpet to reveal the access plate. The top of the fuel pump assy has 2 wiring connectors....one goes to the fuel pump itself & gas gauge, the other one goes to the fuel tank pressure sensor....un plug the pressure sensor...........a few of us have had this sensor( or the wiring to it) go bad .....it is in the same power feed as the TPS and the IACV.....fwiw my truck acted exactly as yours is doing and unplugging the sensor was an miracle cure instantly....you still may need to change the plugs .....but its worth a try...good luck
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Old 12-28-2018, 03:59 PM
mrbieler mrbieler is offline
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alternator was showing low voltage. new alternator, new plugs, new wires, new crankshaft position sensor. fuel pressure tested right. Shop retested cylinders and got numbers in the mid 150s. Shop also confirmed good fuel pressure.

No CEL coming on. No codes.

We've got it running and idling relatively smoothly IF the TPS is disconnected. A new TPS swapped in did not change the situation. Without TPS, it idles at about 2500, gets warm, and settels to a low wandering idle. Plug in the TPS and it stalls.

I'm going to see about having the ECU reflashed and a full diagnostic.
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Last edited by mrbieler; 12-31-2018 at 10:04 PM.
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Old 12-31-2018, 02:19 PM
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pdxrovermech pdxrovermech is offline
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Quote:
Originally Posted by XCELLER8 View Post
ok....try this >>>...access the fuel pump under the rear carpet ( just roll up the carpet to reveal the access plate. The top of the fuel pump assy has 2 wiring connectors....one goes to the fuel pump itself & gas gauge, the other one goes to the fuel tank pressure sensor....un plug the pressure sensor...........a few of us have had this sensor( or the wiring to it) go bad .....it is in the same power feed as the TPS and the IACV.....fwiw my truck acted exactly as yours is doing and unplugging the sensor was an miracle cure instantly....you still may need to change the plugs .....but its worth a try...good luck
Glad I came across this. Have one in the shop that I've been struggling with. Unplugged the pressure sensor and it ran great. I've never ran into this before in my 20 years of working on rovers. I had tried everything else i could think of. The rig had been sitting for a couple years so it was due for a full service anyways, but this one had me scratching my head. Thanks for posting!
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Old 12-31-2018, 11:01 PM
XCELLER8 XCELLER8 is offline
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glad it helped !
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Old 01-08-2019, 03:12 PM
mrbieler mrbieler is offline
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More work done and still no solution. TPS is showing low voltage, but the ECU and all wiring connections, including wires that share leads with the TPS are showing good. No funky grounds, shorts, etc. Thinking of overlaying the wires from the TPS to the ECU. Not sure what else to do at this point. We're drained the tank in case of bad gas, the cats are OK. ECU was swapped and that didn't change anything. This one is a real PITA. Everything else about the truck is solid so I don't want to give up on it, but being a car down has been a real issue for the family. Going to have to get a rental to cover us for a while.
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Old 01-08-2019, 05:26 PM
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Did you check the fuel pump wiring harness?
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Old 01-08-2019, 06:18 PM
mrbieler mrbieler is offline
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yes. that didn't change the idle issue. Something in the ECU connection appears to be wonky. At no point on the harness or at any connection is the voltage low, but at the TPS, it's under 0.5volts. We played with the fuel pump sensor, tps, and ICV. Anytime the TPS was plugged it, it would die no matter what we did with the other sensors. We're going to overlay a new wire from the ECU to the TPS.
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Old 01-09-2019, 08:36 PM
mrbieler mrbieler is offline
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Truck is now running great. Unfortunately, with all the work, battery disconnected, ECU swaps, etc I need to drive it for a few days to get the miles up and make sure the codes clear so I can get it smogged and registered for 2019.
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Old 01-09-2019, 09:10 PM
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So what did you do to remedy the problem?
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Old 01-09-2019, 09:39 PM
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Quote:
Originally Posted by mrbieler View Post
Truck is now running great. Unfortunately, with all the work, battery disconnected, ECU swaps, etc I need to drive it for a few days to get the miles up and make sure the codes clear so I can get it smogged and registered for 2019.

Just FYI, a battery disconnect has no impact on a GEMS ECU. They have no volatile memory, and the way they are wired effectively disconnects the ecu from the battery about 10 seconds after you turn off the car. Listen for the underhood relay click. Thats severing all power to the ECU
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Old 01-09-2019, 09:47 PM
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Idling at 1500-2000 RPMs is pretty common with GEMS. The way I've always fixed it is reset the throttle adaptions. I'm not sure if you can do that with an aftermarket scan tool.
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