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Rough Idle & Check Engine Light

07-31-2004, 01:11 AM
Hello. Today I started up my Rodeo (had already been driven 2X today prior to this) and I got a rough idle with a little shakiness. I started to go and I could feel some trembling in the car and then the 'Check Engine' light began flashing. It flashed for about a minute and then remained solid and remained on.....even after a restart. I did not feel the trembling/shaking once I got the car above 20mph. I did not smell anything and nothing seemed hot and no smoke came from the engine. I checked my oil and it seemed full (but did not look thick on the dipstick...very thin). Does anyone have any idea what this could be? Thanks!
'99 Isuzu Rodeo V6 4WD

Ramblin Fever
07-31-2004, 02:40 AM
O2 sensors, spark plugs, EGR are a few possibilities.

You know, mine did that just yesterday, but not at start up, rather a take-off, just after start up. The check engine light flashed on/off so fast, I barely even saw it. It hasn't come back on, however - but I wonder if I caused the problem myself, as I had let the truck idle for 10-15 minutes on a warm day, then gave it some gas to go and quickly had to kill the power as a car cut me off. :eek7: :mad:

No issues today, however, I still have all the original O2 sensors.

07-31-2004, 12:12 PM
It was the spark plugs. Thanks!

08-15-2004, 11:35 PM
I had this problem 2 weeks ago and had a diagnostic check run. It read that the spark plugs were going bad and misfiring. I had these replaced at $28 a plug b/c I read on here that cheap plugs will result in misfiring even if they are new. Now I am getting the same rough idling and the check engine light has come on again. Could this be that they installed not-so-good plugs or should I be concerned about something else causing this similar problem?

08-16-2004, 08:33 AM
Sound like the intake manafold gasket to me.

08-18-2004, 08:58 AM
I went to Autozone and had my Rodeo hooked up: It was a misfire in cylinder 5. Does this mean it could be a faulty spark plug (they are all new) or could it be the wire? Do all wires need to be replaced if one is faulty? Could it be anything else causing a misfire in cylinder 5?
Also, is it okay to drive for a few days like this (flashing 'check engine' light with a rough idle and some trembling)? I am real busy with work today and tomorrow so it will be difficult to get into the shop (that installed the new plugs) until late tomorrow or Friday.......and I have to use my car a little over the next few days (probably around 75 miles of driving).
Thanks for the help!

08-19-2004, 05:33 PM
I took the Rodeo back to the shop that installed the plugs. They checked the plugs ( Iridium Denso) and the wires?/coils at the plug and could not find anything wrong......ran some other tests and could not find anything. I am getting a misfire in cylinder 5: P0305. They recommended taking it to Isuzu but I'd rather not have to drive an hour and pay $75 for their diagnostics and then pay for the fix unless I have to.
'Ramblin Fever' had mentioned that it may be "O2 sensors, spark plugs, EGR".
But the spark plugs checked out okay. Also others had mentioned the fuel filter or the intake manifold gasket. I also read that a weak battery or dieing alternator could cause problems.
Do I need to clean the EGR ports or something else? Any help would be appreciated. B/T the brakes, the turn signal, the sensitive anti-lock brakes, and now the engine I'm at my wits end with this Rodeo. I'm to the point where I'll probably tell anyone who asks to never buy Isuzu. I understand that there is maintenance to be done at regular intervals, but the vehicle should not just start failing (one thing after another) when it reaches that point........our Honda doesn't. Thanks!

08-19-2004, 05:48 PM
O2 and the EGR will not give a missfire code.

I'm sticking to my guns. It's the Intake manafold gasket.

08-19-2004, 06:27 PM
O2 and the EGR will not give a missfire code.
I'm sticking to my guns. It's the Intake manafold gasket.
Is there a way to test/check the intake manifold gasket prior to taking it in to the shop? I have a full warranty/powertrain warranty up until 100K miles so I'd like to be sure so I can get this covered (assuming it's the gasket I have to call my warranty place prior to taking it to the shop). Thanks Amigo-2k!

08-19-2004, 09:31 PM
you can listen for an air leaking sound around the manafold. ANd you can spary carb cleaner when the engine is running. If the RPM's pick up while, spraying you have a leak then.

I think it is pretty much standard protocol at Isuzu now, if they see a missfire code, the first question is, "did you put in new wacky brand plugs", if not they might swap around the coil on #5 to see if it make another cylinder bad. And if that fails they will swap out the manafold gasket (Super super common, I even had mine changed for free, and I know of others that have had it done 2x already).


08-20-2004, 08:54 AM

Leaking fuel pressure regulator is the common cause:

The original symptom was a Check Engine Light with a #6 cylinder misfire code of P0306 when set at idle, or a random misfire P0300 when set while driving. The #6 was obviously running rich as indicated by the the spark plug. Eventually it became a hard start also. Here's the fix: The fuel pressure regulator was leaking fuel down it's manifold pressure vacuum line. The vacuum line attaches to the manifold right above the #6 port, that's why the richness only in that cylinder.

Fuel pressure regulator part # for 1999 Rodeo: 8-17113-398-0

08-21-2004, 07:06 PM
I bought some carb cleaner spray today and am going to try the technique mentioned above to test the intake manifold gasket. One question though: it specifically says 3X on the bottle to not spray while the engine is running.....though that is the method that is recommended here to test for the problem. I'm assuming I ignore that warning? I just do not want to do any more damage. Where exactly do I spray this and is there anything I need to do prior to spraying? Thanks a lot......again!

08-21-2004, 08:31 PM
I'm assuming I ignore that warning? I just do not want to do any more damage. Where exactly do I spray this and is there anything I need to do prior to spraying? Thanks a lot......again!

You'll have to remove the air filter box and disconnect the airflow sensor attached to the air intake. With the engine running, work the throttle with your hand to open it up some. Spray the cleaner into it but not a lot. The warnings on the can are to prevent excess pressure from buuilding up in the cylinders I think. Too much is too late. Then listen for the RPM change as noted above.
I'd go along with the intake manifold gasket fault suggestion, but it could also be an ignition coil starting to fail.

09-11-2004, 12:34 PM
O2 and the EGR will not give a missfire code.

I'm sticking to my guns. It's the Intake manafold gasket.


Ive been searching for days for this very forum. Ive got the same problem Jovian9 Has, almost to the letter. 97 Rodeo, 3.2, #5 Cylinder misfire code. EGR code. Cleaned EGR, only removed Throttle plate and EGR to do so. Ran a bottle brush along with carb cleaner. Afterwards, went back to Autozone. EGR code went away but.... some Secondary emmisions code pops up. In the onset, I installed non other than Bosch Plats thinking they would do the trick. According to you guys, they may as well be made by MATTEL. So, Ill swap those out for the NGK's. Apparently, I need to check the Intake Manifold gasket very carefully. This thing has about 80,000 mi..... When running properly, it runs like a scalded cat....only would like to adjust the valves. They sound like 50 pairs of teeth chomping up and down. Any other suggestions from you guys would be greatly appreciated. ( Im an old chevy V8 man ) so these rice burners can skunk me.......

09-11-2004, 01:03 PM
Ive been searching for days for this very forum. Ive got the same problem Jovian9 Has, almost to the letter. 97 Rodeo, 3.2, #5 Cylinder misfire code. EGR code. .....
The typical intake manifold gasket issue only applies to 1998+ 3.2's. 1997's are not *quite* as sensative to spark plug brand either- but I'd pull the bosch's anyway (never had good luck with bosch plugs), You have hydraulic valve lash adjusters on your 1997 so you can't adjust the valves. The EGR systems on 1993-1997 is not as troublesome as 1998+ Your problem is probably due to the bosch spark plugs.

09-11-2004, 01:04 PM
I had the exact same problem as jovian myself and sure enough it was the intake manifold gasket but mine went at around 80000 kms

09-11-2004, 05:06 PM
Im going to assume youve been around Izuzu's for a while. This is my first experience, as it is my girlfriends car. She experienced the original problem(rough idle, Poor performance, ) starting about a week ago. I pulled out what looked like the original plugs. Champions, I believe. They were clean as a whistle though a little worn. replaced those, with the wrong plug, I understand. Then cleaned out the EGR passage which was completely stopped up. Even still, I would swear the idle is rougher than ever. Will change to NGK's and take it from there. Probably check injectors and coils. By the way
, anyone know what voltages or ?? Im looking for
on these items. Thanks folks......PB

09-12-2004, 01:35 AM
before doing something you mayu regret on your Rodeo try pulling the #3 and # 5 coils put #3 in #5 hole and #5 in #3 holego back to autozone if not to far see if you get p0303 if so you have a coil problem if not do the same with the spark plug if misfire moves its the plug. I personally have never seen a vacuum leak cause a misfire. By the way just in acse you dont know cyl #5 is on the rear cyl on the pass side drivers side is # 2,4,6 and pass is 1,3,5

09-13-2004, 09:23 PM
After having my Rodeo for nearly 2 days Isuzu figured out that it was an injector that was dirty and had some corrosion. The guy pulled it, cleaned it, put it back, and now the problem is gone. All for the $75 diagnostic fee. It has been running fine for one week now. Should I have the injectors replaced now (d/t this maybe happening again)? Is this an $expensive$ job?
If anyone has been waiting to hear.........Sorry for the delay in the response to this problem. I was out of town for a week and have been busy since I got it did not get fixed until last week.

09-17-2004, 05:49 AM
Anyone following this thread/have simular problem. Went ahead and replaced intake manifold gaskets. Installed Autolite Double Platinums. (Made for this engine) replaced # 5 Cyl. coil. Replacing intake gasket may not have been completely nessesary, but now this thing idles like a sewing machine. The throttle response is awesome! Unless your experienced, dont replace intake manifold gasket yourself. Not that its that difficult....just a lot of details you dont want to miss.


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