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Discussion Starter · #1 ·
Hi all, new member here. Recently bought a 1997 Rodeo V6 4WD w/158K miles. She was in rough mechanical shape so I took her to the dealership and had new plugs and a new fuel filter installed.

I also went to Jiffy Lube (no groans please) and had the following done: oil change, new air filter, transmission fluid change, oil system engine flush, and fuel injectors cleaned. Needless to say, this made a huge difference in the vehicle, but there's still one symptom left:

When I'm driving at about 30 mph, or about 2000 rpm, the engine would occassionally drop it's rpm to about 1500 and then spike right back up. Almost felt like it was upshifting to 4th and then downshifting to 3rd right away. (It's been about 8 years since I've owned an automatic) So I left it in 3rd gear and the problem persisted. I then parked the car, revved it up to 2000 rpm (which was actually quite hard to do as the throttle was really sensitive and difficult to modulate until you hit 3000 rpm) and then got off the gas. The rpm literally dropped to about 200, then bounced back up to 1000 and then proceeded to yo-yo for 3 or 4 cycles before stabilizing at 800 rpm. I also noticed that whenever I ease up on the gas or get off the throttle, the rpm would drop significantly. I had a similar problem with my Audi GT Coupe (actually, it was the opposite and the rpm wouldn't come down) that turned out to be a stuck idle stabilizer.

Any help/info would be greatly appreciated as it's a bit of a haul to go to the local Isuzu dealership so I want to know what they should be looking if possible.

Thanks!
 

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Try spraying some carb cleaner abound the base of the intake manifold, try and rule out if its an intake manifold gasket leak. If there's a leak in the gasket it should raise the rpm a little when you spray it in the right spot. Also, make sure and check for disconnected or bad vacuum hoses or things that should be plugged that arent.
Someone else weigh in too.
 

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Definately check or replace all of your vaccum hoses. This sounds vaccum related. Usually when you get off of the gas and your idle drops like that you have a vaccum leak somewhere. Or everything would be a bit more stable then what you are talking about.
 

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also went to Jiffy Lube (no groans please) and had the following done: oil change, new air filter, transmission fluid change,
You have the 4l30e tranny right? I went to jiffy lube to get a tranny fluid change and they said they could not do it becaues it is a sealed transmission. Id make sure they changed it.

kevan
 

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Discussion Starter · #6 ·
offrodeo said:
also went to Jiffy Lube (no groans please) and had the following done: oil change, new air filter, transmission fluid change,
You have the 4l30e tranny right? I went to jiffy lube to get a tranny fluid change and they said they could not do it becaues it is a sealed transmission. Id make sure they changed it.

kevan
Yup. Come to think of it, they did mention something about the tranny being sealed, but said to come back in a few days because they did change it and that I would be noticing a smell initially from the new fluid. I'll have to check the work slip.

Thanks again!
 

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Discussion Starter · #8 ·
I ended up dropping it off at Precision Auto Tune this morning as they are 5 minutes from my house and when they ran the diagnostic, they found a bunch of error codes, but the CEL never went on. Probably because the CEL light burned out due to the previous owner never getting it checked. Anyways, same error codes that the Isuzu dealership found. MAS, misfire on #6 cyclinder, and something about a quad or other. They pulled the MAS and idle unit out and both were really dirty so that's getting soaked. They're going to have to pull the computer now and see what's going on. This is becoming a very expensive deal. $200 for 2 hours of diagnostic and they really haven't fixed anything. What pisses me off is that the Isuzu dealership never rechecked my car after doing the tune-up. Chances are, they would have caught those codes again. Last time I go to them.

P.S. Just got another call from the shop, the CEL light and airbag light are MISSING!!! Whoever had this SUV prior really @!#%'ed it up. Even the shop manager is having bad feelings about this. Maybe it's time to cut my losses.
 

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Sounds like it's time to write to Isuzu and ask them to reimburse/correct the problems on their dime since they failed to do the work that was paid for.
 

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Discussion Starter · #10 ·
So I called my friend who sold me the SUV and he told me to have Precision Auto Tune stop what they are doing as he knows a mechanic who knows Isuzu's. So, I'm only out $200 for 2 hours of diagnostic and I did learn some more things that are wrong with the SUV. It's time decide if I keep it or cut my losses.

BTW, does anyone know how much a coilpack is for the 97 Rodeo and where I can get one? It would explain some of the problems I'm having, like the misfire even after new plugs were installed. I'd rather not go back to my Isuzu dealership and I was less than happy that they didn't tell me the CEL and airbag lights were missing when they had the dash removed to replace a dash light and didn't check to see if the new plugs took care of the error codes.

Thanks again everyone for the helpful advice. I really would like to keep this SUV as it would be perfect for my needs if it was running right. :?
 

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Just saw a 1st gen coil pack on eBay not too long ago. Might want to check there first, since I'm sure it'll help you "cut your losses" by buying used.
 

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Discussion Starter · #12 ·
Great news. The shop found that a couple of the vaccum hoses were connected incorrectly. I'm not surprised based on what I've seen the previous owner has done to this poor car. Just wanted to say "Thanks a lot!" for the quick response and correct diagnosis to the problem!
 

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coil packs are very exspensive. If i were you id go hit a junk yard for one. They dont go out very often. With 230000 miles on my 93 rodeo, all three work

kevan
 

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Discussion Starter · #14 ·
I knew the fix was too good to be true. Picked up the Rodeo on Friday, drove it all weekend and the symptoms resurfaced (inability to maintain a constaint speed/RPM and the RMP bouncing at lower driving speeds). I was resolved to never figure out what's wrong until Sunday night, driving home, the engine died on me. Took about 2 minutes before I could get it to turn over. Unfortunately, this has happened to me before in my Audi and the culprit was a bad fuel pump and fuel relay. Granted, the Audi was 20 years old w/200K miles. But I'm figuring a 1997 Rodeo w/160K miles probably needs to have the fuel pump/relay replaced? It would explain many of the symptoms I've experienced.

Thoughts anyone? Anything else to replace? Maybe the throttle sensor too? I figure if the tanks coming off, might as well take care of as many related parts/systems as I can.
 
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