2005 GX470 misfires, especially at idle (1 Viewer)

[landobano]

I’ve been getting misfire codes for all cylinders P0300, P0301,P0302 etc when cold starting the vehicle. It runs pretty bad but when it warms up it’s okay most of the time it seems, but can misfire when running and will occasionally die when driving but only at a complete stop while in drive. I’ve also gotten P0171 and P0174 codes for both banks before but I don’t seem to get those anymore after several code clears and resets of the ECU

I thought it was just bad plugs so I replaced the plugs and coil packs so those are all new. That didn’t fix the problem so I tried cleaning the MAF sensor and the problem went away and it ran smoothly for a while, but the problem returned. I tried unplugging the MAF sensor while running to see if it was problem and the engine turned off so I think it’s fine. I also checked for leaks in the intake since I thought it could be maybe unmetered air getting in the engine and no change in how the engine runs when spraying around the intake. The engine does also sound like a vacuum when starting it up cold but I think the secondary air pump is clogged and probably unrelated (no codes thrown for this).

Every time I clear codes and try again the engine runs poorly and throws misfire codes on all cylinders. Looking through other forum posts I see things like maybe cam/crankshaft sensors but I’m not getting codes for those and I put fuel system cleaner in the tank which I’m still running through but at this point I’m not sure what to check next.

Any suggestions on what to try next?

Thanks!

 

[Rednexus]

Does not sound good....off the top of my head, is the timing belt either 1) a recent job or 2) way past due? Wondering if it maybe the timing belt was either installed 1 tooth off or jumped a tooth due to age/wear.

Misfires can also be caused by internal engine problems like burnt valves. Being that you're getting them on all cylinders, a compression check is probably also in order (though it would seem unusual that you'd have misfires on all cylinders).

Edit:
I'd suggest posting this over on the 100-series forum, which has more folks knowledgeable on the ins-and-outs of these engines ,Looks like a few others have had this happen and it was internal engine damage. Definitely suggest a compression test, which should tell you a lot (and hopefully rule out internal engine problems if it's not that).

Multiple Misfires, Codes P0300 - P0306, P358...any ideas?

Hey there, having trouble getting my 06 LC to run. I’ve bought a few new coil packs, swapped them around, but the only code I’ve been able to get rid of was the P358 Cylinder H Coil. The timing belt looks new-ish, and the marks are lined up from what I’ve gathered poking around on this site...

forum.ih8mud.com

 

[landobano]

Does not sound good....off the top of my head, is the timing belt either 1) a recent job or 2) way past due? Wondering if it maybe the timing belt was either installed 1 tooth off or jumped a tooth due to age/wear.

Misfires can also be caused by internal engine problems like burnt valves. Being that you're getting them on all cylinders, a compression check is probably also in order (though it would seem unusual that you'd have misfires on all cylinders).

Edit:
I'd suggest posting this over on the 100-series forum, which has more folks knowledgeable on the ins-and-outs of these engines ,Looks like a few others have had this happen and it was internal engine damage. Definitely suggest a compression test, which should tell you a lot (and hopefully rule out internal engine problems if it's not that).

Multiple Misfires, Codes P0300 - P0306, P358...any ideas?

Hey there, having trouble getting my 06 LC to run. I’ve bought a few new coil packs, swapped them around, but the only code I’ve been able to get rid of was the P358 Cylinder H Coil. The timing belt looks new-ish, and the marks are lined up from what I’ve gathered poking around on this site...

forum.ih8mud.com

Right? It's funny because the engine will run well and smooth sometimes. I actually just got a timing belt/water pump before I did the sparks and coils but it had that same issue before. Yeah the misfires thing is really weird..

I took a look at that link and it'll be probably the third time I've seen the problem being a cam/crankshaft position sensor so I was thinking about trying that next but the OEM parts aren't too cheap. I was possibly thinking maybe the connector for the O2 sensor since cleaning it once fixed the problem for a little while and it was super smooth afterwards. Definitely appreciate the information and I'll to check with those guys too.

 

[Rednexus]

Right? It's funny because the engine will run well and smooth sometimes. I actually just got a timing belt/water pump before I did the sparks and coils but it had that same issue before. Yeah the misfires thing is really weird..

I took a look at that link and it'll be probably the third time I've seen the problem being a cam/crankshaft position sensor so I was thinking about trying that next but the OEM parts aren't too cheap. I was possibly thinking maybe the connector for the O2 sensor since cleaning it once fixed the problem for a little while and it was super smooth afterwards. Definitely appreciate the information and I'll to check with those guys too.

I would try the compression test before any new parts. A tester is only $30 and will tell you right away if you have an internal engine problem, at which point the new parts won't help. Last time I had misfire codes (on a Subaru) it ended up being a burnt valve .

 

[Jstawgn]

Mass air flow sensor can go bad. When they went bad it can cause problems you describe.

Quick quote from Google search
Symptoms of a Faulty Mass Air Flow Sensor

• The engine is very hard to start or turn over.
• The engine stalls shortly after starting.
• The engine hesitates or drags while under load or idle.
• Hesitation and jerking during acceleration.
• The engine hiccups.
• Excessively rich or lean idling.

You need a scanner that can monitor a few things at one.
Long term, short term fuel trim for both bank.
O2 sensor 1 for both bank and Commanded AFR.

 

[landobano]

Mass air flow sensor can go bad. When they went bad it can cause problems you describe.

Quick quote from Google search
Symptoms of a Faulty Mass Air Flow Sensor

• The engine is very hard to start or turn over.
• The engine stalls shortly after starting.
• The engine hesitates or drags while under load or idle.
• Hesitation and jerking during acceleration.
• The engine hiccups.
• Excessively rich or lean idling.

You need a scanner that can monitor a few things at one.
Long term, short term fuel trim for both bank.
O2 sensor 1 for both bank and Commanded AFR.

Completely forgot to update this after fixing but doing so for anyone else who might be having a similar issue. It wasn't the MAF sensor which I had also though previously. I did a smoke test and I saw a huge amount of smoke all around the intake manifold. I determined that the intake manifold gasket was leaking. So I replaced that (it's only $40 online) and the truck runs like a champion now. No codes, runs great all the time, problem solved.


I also wanted to say that I have a scanner for long and short term fuel trims and they were strangely at their normal values from what I remember so I had to do more troubleshooting and that's when I decided to do a smoke test. Both O2 sensors on the vehicle also ended up being good and a AFR also was fun when the vehicle warmed up. Probably the expansion of the metal sealing what the bad gasket left exposed.


Thanks for your help!

 

[Jstawgn]

I am noticing the fuel trim on Bank 2 are always higher 3-5% higher. I might have similar problem with intake gasket although not as bad yet.

Thank you very much for the update.