Here is the problem: when my truck is cold there is an idle surge (goes from 900 to 1500) when I shift the truck in D. If I put the truck in neutral or I stop long enough at a red light, the idle goes back to normal. When I shut the truck off after it warmed up, and then start it back, it idles fine. There is also something bothering me, if I take my foot off the gas pedal suddeenly, the RPM drop down to 500 and then bounces up to 750 (or wherever it needs to be if I'm driving), is my truck the only one doing that? The truck is tuned-up;

-Spark plugs are 2 months old
-Wires are 2 years old (approximately 30k km)
-Throttle body is clean
-Fuel filter is 3 weeks old
-O2 sensors are 1 year old

I also have access to an OBD scanner that reads live data. TPS is fine, a steady 10% when I don't give any throttle, and during the idle surge. Air temp sensor seems fine, it reads around 30 C (what would be the value with a multimeter?), and the engine temp sensor reads fine. There were O2 related codes I forgot, they still have to reappear. What is the normal reading for the MAF?

Unfortunately the scanner I have doesn't give me the reading for the fuel temp sensor. What would be the correct reading with a multimeter? And is there a way to test the IAC?

In the meanwhile, the truck had an episode of not starting when hot. It stayed parked for a week during Christmas holidays. I went to start it a good 10 minutes before I left home (it was freezing cold), went to the gas station, shut it off and it didn't fire up unless I gave it some gas. And I had to rev it constantly to keep it running. Hooked the scanner, cleared the O2 codes, checked some live data while revving it, and at one point it started to idle correctly by itself. I wasn't able to check the fuel pressure, it was dark and I had ti give it throttle to keep it running. I can hear the fuel pump when I turn the ignition on.

I have two hypothesis;

-IAC
-Fuel temp

What are your thoughts on this? Any help is greatly appreciated.

 

Fuel temp sensor - I don't have the values for the IACV test or the FTS here at work but can post them later unless someone beats me to it.

EDIT - Found it for the IACV - coil resistance should read between 40 & 70 ohms but this info is from my notes on a '95 MY and I can't remember if it is the same values for your year. Soooo I'll still check when at home tonight.

 

Thanks

I'm working on the truck right now. I found a leak in the air intake hose, the o-ring between the air filter box and the MAF was missing. I put one back in but didn't test the truck yet.

I also checked the IACV for carbon deposits but I had no luck, it was sparkling clean. I'll have a multimeter later on today. I'll post my results ASAP. What is the normal reading for the MAF when hooked up to a scanner?

I also forgot to add, the truck failing to fire up was only a momentary episode. I went wheeling last week-end; lots of shutting off and start ups and I had no problem whatsoever.

 

These values are only for Gems ECM's-

IACV - both circuits should measure between 40 and 60 ohms
circuit 1 is pins 1 and 26
Circuit 2 is pins 28 and 29

MAF output voltage - 1.7 (idle) - 4.5 (full throttle)
(Disclaimer on this one---I think!!!!! Those are the values for the 5AM but gems uses a 20AM SAGEM)

TPS
throttle closed - 0.6 v
throttle open - 4.5v

ECT
0.7v @ 185*F -----V will increase at temp decreases
28,000 homs @ -22*F
300 ohms @ 185*F ----Normal op temp.
90 ohms @ 266*F


IAT *[note - ignition timing retarded above 131*F]
23,000 ohms @ -22*F
290 ohms @ 176*F (hope you never drive in those conditions )

Fuel Temp
1,100 ohms @ 104*F

Oxygen Sensors -Titania Type (narrow-band)
.01 to 1.0v (supply voltage from ECM 5v... mix determines resistance which drops v accordingly)
high volts = rich
low volts = lean

I know you didn't ask for all that but there it is anyway.

 

Thanks for all these values. If they are not in the sticky section it would be a good thing to add since most people perform diagnostics themselves on their trucks.

I was working on my truck at my parent's since I don't have a garage at home and my dad came back from work pretty late last night so I wasn't able to borrow his multimeter. I'll try to squeeze a small time frame to do the tests on Sat. I don't want to freeze my **** off doing these outside at home.

The CEL reappeared on my way home last night, so I'll hook up my scanner later today to get live data when cold and when hot.

 

I just hooked the scanner and here's what I got:

2 CEL codes; P0158, P1193

Data ;

Idle: between 975-1000
Coolant temp: -9 Celsius
Intake air temp: -7 Celsius
ST fuel trim B1: 0%
LT fuel trim B1: steady 4,67%
ST fuel trim B2 : 0%
LT fuel trim B2: steady 4,67%
Ignition timing: ± 33 degrees
MAF: 0.14 g/s
O2 B1 S1: 0.01v to 0.98v STF ± -3%
O2 B1 S2: 1.01v
O2 B2 S1: 0.01v to 0.98v STF ± -8%
O2 B2 S2: 1.01v

Data when hot;

Idle: between 685-720
Coolant temp: 81 to 86 Celsius
Intake air temp: 12 Celsius
ST fuel trim B1: 1.55% to 6.23%
LT fuel trim B1: steady 4,67%
ST fuel trim B2 : -0.79% to 3.11%
LT fuel trim B2: steady 4,67%
Ignition timing: ± 27.5 degrees
MAF: 0.06 g/s
O2 B1 S1: 0.01v to 0.98v STF 5.45% to 7.02%
O2 B1 S2: 0.53v to 0.9v
O2 B2 S1: 0.01v to 0.98v STF 3.11% to 6.23%
O2 B2 S2: 1.01v

This is the only data I can gather with my scanner. The faulty O2 would be Bank 2 sensor 2. Which one is it? Passenger side post cat? Though I doubt the idle surge is due to this O2 being bad.

I searched in RAVE for normal reading values and I found absolutely nothing, except voltage values.

 

Rear O2's do nothing other than tell the ECU that your cats are working or not.
I have nothing else to offer on this one, sorry.

 

I haven't driven the truck much since my last post, but so far, everything seems to be back to normal concerning the idle surge. Putting back the MAF o-ring seems to cure the problem. I'm not convinced yet, because temperature has been unusually warm for the last couple of days.

The only thing still bothering me is that when I lift my foot from throttle, the truck struggles to adjust its idle speed. It drops low, around 500 and then bounce back slowly to around 750. I'm leaning towards IAC for this one. I'll try to clear a little time to check it with a multimeter to see what's going on. I'll report back as soon as I have something new.

 

It's a shame the IACV is so expensive. Before mine went totally bad, it started acting "funny", like it would hunt for the right spot for correct idle, and it was really sluggish when cold. Did that for a couple months then completely sh*t the bucket and didn't work at all and would not idle under 1200rpm.

 

The IACV from a Jeep 4.0 is a exact fit.
However if you need it programmed by the dealer they will not use it, they will install a Rover IACV.