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1999 Isuzu Rodeo V6 Erratic Idle/Stalling/Hard Starting

02-13-2005, 12:38 PM
One year ago I had the following problems that were fixed by replacing the fuel pressure regulator (I did a write up on this forum on how to replace it and will gladly furnish that info to anyone who needs it):

1) Erratic Idle
2) Frequent stalling at idle
3) Hard starting - (have to give it gas)
4) Intermittent CEL light - gone

Now, 1 year and 15K miles later, I am having similar issues once again. When cold it is very hard to keep running and will die at traffic lights etc... unless I keep the clutch in and baby it. When cold the idle fluctuates wildly. Once up to running temp. and after sitting for about 15 minutes not running, I can start it easily and then drive without babying it. Sometimes the idle will then be fine, and other times it will fluctuate, so the problem is somewhat intermittent but getting worse when cold.

I am considering replacing the fuel pressure regulator again to see if that helps before bringing it to a dealer to have the diag. run.

It seems strange to have the fuel press. regulator only last 15K mi., and it also seems a little strange that it seems to run better (for now at least) once it is warm, but, the regulator "is" located where it does get nice and warm and perhaps that changes the properties of the diaphragm it uses to control pressure. It would be a cheap fix again if that was it, but, we all know how well wishful thinking goes in these situations.

Input anyone? Any feedback greatly appreciated. I got incredibly great info on this forum last year.

Also, does anyone have any new info on whether there was ever a recall on the sending unit that controls the fuel gauge?


02-13-2005, 01:17 PM
Sounds like the intake manafold gasket.

Once it warms up the holes start to close up.

02-13-2005, 01:23 PM
I agree sounds like intake gaskets leaking.Since yours is that bad you could try spraying some carb cleaner around the intake while it is acting up and see if the idle changes.Just to make sure.But I think they are probaly bad.When you remove the intake you will see they are broken.They are almost a plastic type of material.Carl

02-13-2005, 01:24 PM
Definately symptoms of a bad IMG. Do a search on it & you will find MANY posts.

02-13-2005, 03:06 PM
Makes sense. Seems to me you indicated last year that that is a pretty common, right?

I guess there are likely metal inserts in the gasket around the ports that leak eventually and close up once heat expansion takes place?

It sure looks like it should be covered under my extended warranty, BUT, I'm sure they'll want some cash for running the diag first.

I'll also check the local auto parts stores to see what the price is on the gasket. I took a look at the engine and it doesn't look like it would be too tough of a job as long as you're able to get the throttle linkages etc... all hooked back up correctly. Have you ever changed one out?

I really appreciate the feedback. I'll do a little more hot and cold experimenting and see what I can work out with the dealer and the warranty tomorrow. I'll let you know what I find out. If it is the intake manifold gasket, I'll take a close look at the one that's removed and let you know what I see.

Many many thanks for your input.

02-13-2005, 03:09 PM
Thanks everyone. I'll definitely let you know what I find.

Much appreciated.


02-13-2005, 05:53 PM
Your extended warranty should cover it.Just read it carefully.Some of them don,t cover gaskets.Carl

02-14-2005, 01:27 PM
Sounds like the intake manafold gasket.

Once it warms up the holes start to close up.

Yeah....That's what I'd say. The heat may be causing just enough expansion around the leak to seal it up enough to keep the car running. That would explain why it runs all right when warm but rough when cold.

02-14-2005, 03:59 PM
I've got more data. Believe me, I'm not trying to get around changing the IMG. Not at all. I just wish that it would break completely so that I could pinpoint the cause before tearing into it. Last year it acted this way and it was the fuel press. reg.

Check this out and see if you still think it could be the IMG. This problem has been intermittent over the past few months, and seemed to be really getting worse over the last few days especially when it was fully cooled off. Then, even when warm the idle would be erratic much of the time.

Yesterday I let it sit for 8 hours and then started it at 10pm. It ran really well. No gas pedal required when starting it, and idle was solid. I drove 20 miles, and everything worked great.

Then I let sit overnight and fully believed that it would be a problem this morning, but, it started great, ran great, idle steady as a rock.

If my IMG was bad, it seems to me that the problem would be much more consistent, but, stranger things have happened. It won't do any good to drive 25 miles to the dealer for a diagnostic when it's running fine. I even had it smogged last week and it passed with flying colors. Seems to me that it wouldn't with a bad IMG.

I hope it's not something electronic that's going to die at the worst possible moment, or that it's not something maybe moisture related, or a flaky connection in the fuel pump relay etc...

I was hoping to be able to hear some hissing this morning so that I could narrow this down.

Does it still sound like the IMG?

Any input very much appreciated. As you know, intermittent problems can be very tough to nail.


02-14-2005, 04:11 PM
yup it still sounds like it to me.

When I had my IMG replaced I brought it to the Isuzu dealer for another problem. They said that they put their code reader on and it came up with a code that pointed to the IMG so they replaced it.

The only weird thing it did before they changed it was that the RPM fluxuated about 50-75 (just a little wiggle in the needle) when the truck was warm. I didn't think anything of it, after the IMG was replace the wiggleing was gone.

IMG problems can come and go due to the size and location of the break in the gasket. Under certain conditions it can seal itself for operation under cool/warm and hot use. Other times it doesn't matter what the temp is.

02-14-2005, 05:49 PM
There is a service bulletin,not a recall but a bulletin.But you are right there is no need to drive if they can,t verifie the complaint.I never have removed the intake completely when doing them.I lift it high enough to get them in.When you lift it up you can see where they are broken.It a plastic type of material sandwitched inbetween two pieces of metal.Carl

02-14-2005, 08:16 PM

Do you work at an Isuzu dealership? just checking there are a couple other Isuzu techs here too.


02-14-2005, 09:11 PM
From 1993 to 1997 I worked at Honda.From 1997 to 1998 I worked at Isuzu and kia.From1998 to 2001.I worked at honda.From 2001 to 2002 went to ford.From2002 to 2004 I went back to hondas.In aug of 2004 I opened my own import shop.I don,t claim to know everything but I try my best to help people when I can.Thanks for asking Ryan.Carl

02-14-2005, 09:14 PM

Thanks for the info! Please stick around!

02-14-2005, 09:16 PM
Thanks,Ryan are you an Isuzu tech?

02-14-2005, 10:20 PM
Nope, just a guy that has been reading this Isuzu boards since 1998.

And I went to Moab with a bunch of other Isuzu owner (75 of them) in 2001.

Rental Trooper in Moab:

02-15-2005, 05:24 AM
Awesome picture,I,ll check with you guys later.Carl

02-15-2005, 12:01 PM
Thanks for all of the info everyone. I was just checking out the IMG removal and installation in the Rodeo service manual(s). It doesn't look like too difficult a job. I was hoping that they would show a picture of the gasket, but they don't.

Just curious, is it one big gasket, or does it come in two or more parts (one for each side?)?

Since you mention Carl that you don't fully remove the intake manifold when replacing them, but instead lift it just high enough to get them in it seems that it isn't just one big gasket. Any further info appreciated. I want to make sure I have everything I need before I start. Looks like it would take a couple hours?

I'm off to find the best price/availability on the gasket.

Yep, that is a cool pic Ryan.

Back soon.

Huntington Beach, Ca.

02-15-2005, 12:52 PM



photos from this post:,f86,&Words=IMG&Searchpage=1&Limit=25&Main=630907&Search=true&where=bodysub&Name=&daterange=1&newerval=2&newertype=w&olderval=&oldertype=&bodyprev=#Post677759

02-15-2005, 01:58 PM
Mark,This is going from memory,like I stated early I haven,t worked at dealer since aug.So I can not look at one to make sure I am not missing something.
Remove the plastic cover.Disconnect neg battery terminal.7/8 erg pipe pass side rear,the four throttle body bolts,I leave the hoses hooked up so you don,t make a mess with coolant.The pain is 5mm allen head bolts at the fuel pressure reg.You don,t have to seperate the upper and lower,just pick up the bottom.I leave the fuel line hooked up because it is a pain to release.If you have someone to help lift it up would help.Then I lift up the intake replacing one side at a time.
I think that is everything.I hope this helps.Of course torque to specs.Carl

02-15-2005, 02:00 PM
Oops,that is egr pipe not erg.I lift it up just enough to get them in.Carl

02-15-2005, 03:10 PM
Great. Thanks for all of the info and the pics. Priceless. I'll give an update soon.

Can't thank everyone enough.


03-20-2005, 04:28 PM
Well, I'm finally back in off the road. It's been a little over a month I believe since my last entry on this. I haven't done anything yet since the problem only rears it's ugly head very briefly every two weeks or so. The local dealer has the IMG for $23 so I'll pick that up this week and hopefully get a chance to change it out next weekend.

Still sounds like the IMG, right?

Many thanks,

03-31-2005, 01:10 PM
I picked up the IMG's (lower one between IM and head), part number 8-97237538-0, $23 each side, from the dealer. Their construction, a composite or plastic material about 1/8" thick sandwiched between two metal plates, clarifies in my mind how they could definitely be problematic.

I am currently not having the wildly fluctuating idle and stalling problem, and my gas mileage is really good. As soon as the problem re-occurs, even slightlly, I will change them out. I will provide feedback on the fix including the condition is of the gaskets I remove.

Until then.


04-10-2005, 02:28 AM
I have recently encountered two problems with my pickup:
1. Upon the vehicle warming up, when you cut it off, it will turn over but
will not start up. If you let it sit for about 1 to 2 hours, it will start
and run as if there was never a problem. I have replaced the fuel filter,
mass air flow sensor, air filter, oxygen sensor, distributor cap, rotor,
wires, and plugs. I performed a computer self diagnostic and detected no
problems. I placed a fuel pressure gage in line with the fuel pressure regulator and I am getting over 60 psi (vice 42 psi max) when the engine is running. Upon troubleshooting, I determined that I can duplicate the original discrepancy at any time, if I relieve fuel pressure to the gage by removing then replacing the fuel pump relay. Eureka it is the fuel pressure regulator! Right? Now the plot thickens. If I tap the fuse box in the engine compartment, the pickup will immediately crank however, the fuel pressure will still peg out my 60 psi gage. I swapped the headlight and fuel pump relay (same part numbers) and the problem doesn’t change. I am still focused on the fuel pressure regulator as the problem. I think the abnormally high pressure that the pressure regulator is supplying to the fuel system is causing the ECM to send erroneous signals to the fuel pump relay. I will be purchasing a regulator tomorrow, any suggestions will be appreciated. I noticed some earlier posts in reference to the intake manifold gasket causing idling/stalling problems. Could that be my problem?
2. Upon applying brakes, I physically feel the brake pedal gradually
losing pressure and sinking to the car's deck. Unless I pump the brake
pedal 2-3 times to build up pressure, the brake pedal will continue to
sink, and I will eventually lose braking power and roll forward. I have
replaced the front disc brake pads. The rear drum brake pads do not appear
to be worn beyond specifications. I have generously bled all brakes.
Visual inspection of all brake components has revealed no leaks. I am not
losing brake fluid from the master cylinder.

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