2007 Grand Vitara - random rough idle + hard start

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Bought the car at 130k miles, passed CA emissions perfectly. This is the 2.7L V6 RWD model. Good service history with regular oil changes and thermometer change. I've had the ATF fluid and differential fluid flushed as preventive maintenance. I've changed the spark plugs, the air filter, and cleaned the MAF. Oil is Castrol 10w30 high mileage oil with a Motorcraft filter.

At around 133k miles, car would randomly have a vibrating rough idle, CEL. The CEL was P0401 which pointed me to EGR valve. The car also randomly became hard to start at this point without tapping on the gas as I was cranking it. Had to replace a battery at this point although it was on it's way out anyway. What is strange is that this randomly happened sometimes and not always. I would say about 10% of the time it was super hard to start and shook on idle. Once you're going, it's totally fine, no loss of power, average fuel economy but when stopped and idling, it was rough.

I had the EGR valve replaced, problem seemed to go away. Then it started happening again a couple hundred miles later. This time I'm getting P0401 and P0420.

The second code details Catalyst system efficiency below theshold bank 1

Could it be O2 sensors or is there something wrong with the CC?

Right now, it seems to be running fine, I'm running a dose of Gumout HM Regane through it and maybe one more dose on the next tank. What is troubling is that it's random. Most of the time, it works perfectly normal with smooth idle. I hope when it happens again I'm in a position to right away bring it to the mechanic because this problem occurs randomly...
 
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check the intake hose as it enters the engine. My step-daughter's developed a split that was letting unmetered air in and caused rough idle, stalling and hard starts. Had to reach underneath it to find the tear.
 
The fact you replaced the EGR and the problem went away then came back later is very informative, there is more to the EGR system than the valve.
they may not have cleaned the passages when replacing it, which makes it an area of suspicion because you have no other EGR related codes. What are the fuel trims on this engine? Look at this.

https://www.autocodes.com/p0401_suzuki.html
 
Originally Posted By: meep
check the intake hose as it enters the engine. My step-daughter's developed a split that was letting unmetered air in and caused rough idle, stalling and hard starts. Had to reach underneath it to find the tear.


Yep, while I was trying to clean the intake throttle body, I tore this boot. I replaced it with a new OEM one.
 
Originally Posted By: Trav
The fact you replaced the EGR and the problem went away then came back later is very informative, there is more to the EGR system than the valve.
they may not have cleaned the passages when replacing it, which makes it an area of suspicion because you have no other EGR related codes. What are the fuel trims on this engine? Look at this.

https://www.autocodes.com/p0401_suzuki.html



I know I've run into this with some ~1998-2002 Isuzu 3.2/3.5s I used to maintain years ago. The EGR plumbing would dump out into the intake manifold through a metal tube. The end of the tube would crust over with carbon given it was blasted with cool air downstream of the throttle body. A piece of wire and some intake cleaner spray worked every time for me.

You could remove the EGR valve and fish through the vacuum side port in the valve base if that works for you.
 
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Getting to the EGR is a big job in this engine unfortunately.

RIght now, the car seems to be running perfectly again, maybe the Regane HM is doing something? I am planning to run VR Motorsport fuel cleaner and Regane One and Done and see where I'm at after an oil change.

If it happens again, I guess I'll ask about cleaning out the EGR pipes.
 
Originally Posted By: FlyPenFly
I am planning to run VR Motorsport fuel cleaner and Regane One and Done and see where I'm at after an oil change.


Walmart TLE has a good fuel system cleaning service for $20. There's an in-tank additive poured in then another that's sprayed into the intake. One of the guy's on here works at one is how I found out about it. If you get an oil change there for $29 the fuel cleaning is an extra $10.


 
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