About a week ago my check engine light turned on. Now my 98 rodeo 4WD V6 has an erratic idle (rpm needle jumps from below 1 to almost 3) when ever I turn it on and if I don't leave the engine rev'ed above 1000 rpm it stalls. I took the car to Autozone to have the codes read and they told me that coil number 3 is misfiring and both O2 sensors are bad. I can't remember the actual codes. I was told to change the spark plugs just incase but nothing changed. Should I change everything or is their something else that can give these readings.

A bad Intake Manifold Gasket will cause it and is most likely the problem. Its a common problem on '98 and '99. Isuzu has lowered the torque spec on the intake a few times to prevent it from happening as well as redesigned the gaskets (originals are some kind of thick plastic).

Also a dirty/clogged Idle Air Control valve can cause the eratic idle but not sure if that would throw the same engine light codes as a manifold gasket.

if the vehicle has a misfire for #3 cylinder you need to fix this first then worry about the o2 sensor codes, they could be set due to a misfire, if you swap the coil #3 (in the middle passenger side) with #1 coil see if it moves with the cylinder if it does then replaced that coil in not then look at an injector spray pattern

Well It seems the problem was the intake manifold gaskets. I just finished replacing them and when I turned on the truck It ran better than ever. The Idle was perfect, the check engine light did not come on, and the truck ran perfect. Just want to say thanks for all of your help.

How difficult was the Intake Gasket to replace?

It was fairly simple, about a day and a half but that was because It was really cold and windy those days so I kept going inside for breaks . I also have the repair manual so that was helpful but if you dont have one you might want to check this out http://isuzufaq.ibctech.ca/#faq5

i had that same problem 2001 rodeo ls 4wd , intake gasket manifold. same diagnostics from the computer. I learnt the hard way, by replacing both o2 sensors before bring it in to the dealership

Hi every body, could You let Me know if the intake manifoldgasket, give You an intermitent up idle to 1400rpm.


I have been with this problem for about an a Year. already bought twice the iac valve and one EGR valve and the problem still intermitent, I running My Rodeo 98 at the beginning run ok and suddenly the RPM goes to 1200 or 1400rpm, I need to get the engine goes to warm or cool and the rpm get normal again.


NEED HELP..


THANKS IN ADVANCE ....

Hey guys, im experiencing similar issues. The idle had gotten so bad that the car wasnt turning over anymore. So i ended up pulling the upper manifold off and replacing all 6 injectors, fuel filter, and gaskets. The car still wasnt starting so i swapped the Throttle Position Sensor and it fired right up and was idling normally. However the check engine light was still coming off and the error code read that the car was running lean. About a month later, the car starting idling high again so i replaced the TPS again and it ran fine for a few more weeks and now its doing the same thing again. I dont want to replace the TPS again becuase i think there is something else thats at the root of the problem. If i unplug the TPS though, the car drops down to normal RPMs so im really confused. Also, ever since i pulled the upper manifold off and replaced everything the car takes a few extra cranks to actualy turn over and start. Not sure if thats related or not...but what else can I try to diagnose this issue??

My upper gasket went bad about 2 years ago. The lower went bad about 6 months later. Try replacing the lower gasket. A trick that a friend of mine told me to do was start the car and get a can of carb cleaner and spray the gasket where the manifold halves meet and where the lower manifold meets the engine and if the idle changes you have a leak. As soon as I started spraying the idle became almost normal and when the liquid evaporated the temporary vacuum seal left and the car had idle problems again. Be for-warned the second time I had idle problems I took it to a mechanic and he told me there was a hairline crack in the manifold and it needed replaced with a grand total of $2200! I took it to someone I knew and had him do the upper and lower gaskets and the problem was fixed for $500! So if a mechanic wants to replace the manifold tell him to do the gaskets and only the gaskets first!