H3 H3 "almost dies" right after start up PLEASE HELP

[Jayhawk1525]

This is my first post on this forum site. I love the site and it has helped me on numerous occasions so I thought I would post my own problem to try and get some feedback. I have a 2008 H3 with almost 52,000 miles. For about the last year or so, occasionally (and I stress occasionally) my H3 would nearly die on me right after I start the car. This has gradually increased to the point now where I am holding my breath every time I start the car. It starts up clean and gets to about 1,000 RPM like normal, but about 2 seconds after the start, it loses a lot of power and almost dies on me. A few times it has actually died and I had to do a complete restart, but most of the time it just drops fast to about 200 RPM and with my help pressing the gas pedal down, it jumps back up and hovers around the normal 900 RPM. As I said before this has been going on for a year. My brother used to have an H3 that would do the same. Last weekend with the help of this site I took out my throttle body and MAF sensor and extensively cleaned them both (throttle body was pretty dirty) which seemed to help with the start up, but it is still having a problem. It doesn't happen every single time I start the car, just usually when I haven't driven it for a while and the engine is completely cold. I plan on taking it to Advanced Auto sometime this week to do a battery check, but at this point I no longer know what to do. Aside from the problems at the start the car runs great. I am hoping that it is not a cylinder head problem as I have seen on these discussion boards that replacing those can be very expensive. Has anyone else had a similar issue? I love the car and I want to be able to keep it for a long time so getting this issue resolved is a necessity. Please help!

 

[SuperBuickGuy]

get someone with a tech 2 scanner to read the codes.

 

[amrg]

I've had a similar issue on my Alpha, turned out one of the sensors on my O2 sensors on the manifold was dead and giving false readings. My truck would die whenever I idle!

 

[Best4x4]

Yeah get the codes read if you can to see if you have any pending codes if the CEL isn't on. Honestly though from the sound of it I'd say MAF, Throttle Body or accelerator pedal assembly.

 

[4speedfunk]

You failed to mention if it throws a code. That can help diagnose it for sure.

Your issue seems to be occurring at idle, so it may be related to engine vacuum. One thing I have found to be troublesome is the intake tube assembly. Make sure the hoses do not have any holes, and all the clamps are tight...from the airbox to the throttle body. Any air leaking between the MAF and the TB will make the L5 shake like a crack-baby. I have pulled mine loose accidentally by revving the motor in reverse, and it will demonstrate the symptoms you are describing. Also check the intake gasket. Sometimes the intake bolts are loose and/or completely missing!

Air leaks are easy to detect: While the truck is idling...spray some WD-40 around the base of the throttle-body and along the sealing surface of the intake manifold (where it bolts to the head). Listen to the motor, and see if the RPMs surge when you spray it. If so...it means you got a vacuum leak, and the WD-40 has temporarily sealed it. You can use carb cleaner, or even a plant sprayer with water. Anything liquid will seal the leak and generate a spike in RPM. (I have also used an incense stick, and seen the smoke get sucked into a vacuum leak). Modern electronic fuel injected motors will often adjust themselves to compensate for a vacuum leak....so they tend to mask this relatively simple problem.

Other common items you should check are:

Motor mounts (yes...they can make the L5 stumble)
Battery cables (especially the ground)
Fuel pump (not likely at 52K miles)
Coil Packs (real common)
Oxy sensors (also not likely at such low mileage)

On late-model electronic-a-fied vehicles...sometimes its best to wait for a CEL code to be generated. This will point you in the right direction to make a repair.

 

[amrg]

My O2 sensors where shot at 30K miles, which was weird but had em changed back when I had warrenty!

 

[SedonaBound]

You need a scan with Tech 2 reader; preferably a real GM unit. That you're not getting any Check Engine light makes it harder to isolate. Sounds to me likes it could be a fuel delivery issue; pump or filter.

 

[Reloader]

GM has had a ton of problems with throttle bodies on V8 engines. You didnt say if your 3 is an Alpha or not but sounds like it could be a throttle body issue .
I got a notice from GM a while ago stating that GM was extending the warranty on this issue and would reimburse if customer had paid for replacement out of warranty.
Zach would know a lot more aboot this.

A good diagnostic with a high end scan tool to see what the O2 and other sensors are doing would be the first place to start. Sensors can have intermitant drop outs causing problems that only a good scope can catch. This will also show what the TPS sensors (there are 2 in fly by wire throttle bodies) are doing. A drop out or glitch can cause your issue. You usually cant replace the TPS sensors thus necessitating t-body replacement.

 

[Bigunit]

Reloader, what is a good, high end scan tool that you would recommend?

 

[Reloader]

Someone with a snapon Verdict or a Verus. A Tec 2 would be the best as its the GM tool but it might be the Tec3 now. These are expensive and usually owned but the shop but some techs purchase their own. Independant shops can get the tec2 but not sure about the tec3 yet. The shop I last worked in had a Snapon Verus that cost $12K but it was worth it. An awesome tool.
There are other brands also. Mac Mentor and Navigator . These are built by OTC.
The Verus allows you to look at all 4 O2 sensors at once while you take it out and pound on it (test drive), disconnect individual cylinders, and much more. Many scan tools will do these things so a Snapon brand unit isnt necessary. Sometimes it can take many miles of test driving to get something to act up to find the problem.
There are some code readers out there that will read live data but a scope can really help catch the tough ones.