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Amedee, Former ASE Master Tech
Category: Car
Satisfied Customers: 26451
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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Suzuki Grand Vitara: 2006 Grand Vitara, has an intermittent

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2006 Grand Vitara, has an intermittent low idle miss that occasionally set off the check engine light and will stall the car. I have had 2 different dealers run diagnostics on it and no one seems to agree what will fix the problem. At normal driving speeds it runs great and with 193,000 miles on it we still get 22-25.3 mpg. highway. The codes thrown say dirty/clean egr valve, miss in #2, 3, or 4 cylinder, cat conv on port side failing, weak post port side O2 sensor, & ignition coil.
So I replaced the plugs with originals and replaced the ign coil for the misfiring cyl and replaced an injector that "was said to be weak". One tech said that the cat was backing up the exhaust and causing the miss. I just got back from a 3500 mile trip to Nv and it ran great until I got almost home. (gas mileage on highway 23-25+). When I got to Memphis the check engine light come on and it ran great at high speeds but wanted to stall at idle or stop in or out of gear. Throttle body has been cleaned and injectors have been treated with sea foam. This only happens on occasion but is frustrating on what to fix. I can't do a $3000 exhaust sys. and then have the same problem. Any advise or where to start to eliminate the problem?
Jerrold Cavasin
Hello and Welcome to Just Answer!

IS the engine misfire or rough running condition only at idle?

Does it accelerate good?

What is the engine vacuum at when the engine is at idle? How about at 2500 rpm?
Customer: replied 4 years ago.

Ok lets know that I am not a mech first. I am a retired bricklayer and not able to do the tests even though I have an old vac gauge that has not been calibrated in 20 years. I do not know where to attach it anyway. If you could let me know I could do it. The miss fire is only at idle that I can tell. If it was at a higher rpm the gas mileage would drop and it's at the top of it's game. It accelerates like a beast for a 2.7 6 cyl in a 4x4.

Mostly happens when on a new tank of gas. If I pull the battery and reset the system it will usually stop the problem but this last time it didn't. It still settle's into a rough idle and sometimes stalls. As for a vac leak if there was one at idle wouldn't it get worse at a higher rpm? I have thrown more money than I care to at the dealers to guess on what is going on. Seems like if I replace the ign coil on the missing cyl it straightens out for a while but that could just be coincidence because I replaced one and it lasted about 1200 miles then started to miss again but cleared up when reset.



Thanks for the extra detail!

Was the fuel pressure checked?

Can I get the code numbers in the computer?
Customer: replied 4 years ago.

Fuel pressure checked by first dealer in Aug. They replaced an injector on #4 cyl. That wasn't the prob. I think that they must of checked fuel pressure before they replaced said weak inj. I will go out and see if I can find the codes on a receipt. From Auto Zone the codes are PO302, PO303, PO430, PO101, PO401. The dealers didn't list any codes on the receipts that they gave. Hope this helps.


I am going to be completely honest with you. I do hope you appreciate my honesty. It is best for both of us.

First, there could be a few different things going on with your vehicle. There also could be just one thing causing all of these codes. Just keep this in mind.

Second, There are several possible causes for each code. That means we are looking at several different possibilities here because of all of these codes.

The best way to go about this is to clear the codes and see which code comes back first. Then diagnose and replace or repair one code at a time.

Based on my experience, this problem you have is going to be an air or a vacuum leak causing your idle issue. The reason is happens at idle is because engine vacuum is at its highest point when the engine is at idle. As you open the throttle plate, the engine vacuum goes down. Engine vacuum is negative pressure. So that means as it equalizes with the outside air pressure, there is less engine vacuum. That is why it goes down under a load or as you open the throttle. So any air or vacuum leak, it is more noticeable at idle and lower RPM's.

Another possible cause could be a plugged converter. Did you replace the converter?

In addition, you could have a fuel concern. I don't know off hand, bit if this engine has a fuel pressure regulator located on the fuel rail, it could be leaking fuel into the engine causing this idle issue. It will not affect the engine so much at higher rpm's.

You can check for plugged exhaust using a vacuum gauge or a exhaust back pressure tester. Engine vacuum should be the same if not more at 2500 rpm in park than at idle. If you check exhaust back pressure, it should be no more than 1.5 psi at 2000 rpm in park.
Customer: replied 4 years ago.

Thanks I guess that I never thought that it could be a vacuum leak because all the lines look good. Also I was told by one dealer that the cat conv on the port side is not functioning fully. But wouldn't this cause all the plugs on that side to misfire instead just one or two?

On the old cars (pre 80's) we used to check for vac leaks by spraying the lines with starter fluid. If the rpm went up we found the leak. Can this still be done? or is the starting fluid not safe to use any more? Also can a vac leak be intermittent? Bear with me on these questions. I will go our and wipe the computer then have it rechecked. Is there a way to get back to you after I have that done?


The converter can and will cause the engine to misfire ONLY if it is plugged up. If it is just bad but not plugged up, then it will not cause the engine to misfire. Make sense?

YES.. you can in fact still check for vacuum leaks using carb cleaner or something flammable like that. This can be done.. I do it from time to time. However, this can be dangerous so I don't recommend using this method. Your best bet is to get the intake system smoke check for vacuum leaks using a smoke machine with the engine off.
That is much safer.

YES.. we can continue this conversation even after you leave me with a positive rating. I will continue to work with you until you are happy at no further cost.

Amedee and 3 other Car Specialists are ready to help you
Customer: replied 4 years ago.

Just wiped the computer and drove to Auto Zone for a reading. Absolutly nothing wrong or no codes showed up. Manager suggested cleaning the throttle body so I did. Idle restored and no more problems. Thanks for the help.

Later Gater


Thanks for the update!

Best Regards