jfmjr

I am having a recurring problem that was better for a while but is getting progressively worse. Upon cold start particularly in he morning my 430 idles rough and bobbles for a minute before the engine idle kicks up. For the first few minutes I have to work the throttle a bit as it bucks and stumbles as if it was not getting fuel. Any ideas? I have had several mechanics try to diagnose and no luck. No codes and no check engine light. Any help is much appreciated.

VVTiBob

when was the last time the throttle body and MAF sensor were cleaned?

kjcole

Also could be a leak in PVC hoses - having to feather the throttle to keep it running until just a little warm is classic, but you'd think that's where the mechanics would go first since it is basic 'tune-up' stuff. If true, the issue isn't lack of fuel, but too much air for the computer to correct the fuel/air ratio for cold running, when you need a 'richer' mixture.

VVTiBob

Great point Kelly! And, a simple inspection will tell right away if one of the vacuum hoses is dislodged. But your also right about where a mechanic would or should look first. However the OP states they have not seen any check engine light, or had any OBDII 440 thru 446 codes thrown.
The OP should read through this thread on EVAP vacuum issues and check the hose pointed out in post #13. As well as looking for brittle/cracked vacuum lines and the smell of gas in the cabin.

kjcole

I've had cars where vacuum leaks in the PVC system caused cold stumbling and didn't throw codes! Not sure how sensitive the Toyota code system is for this feature. Besides cleaning the MAF and making sure that are no leaks in the air supply plumbing, I'd follow the vacuum hose inspection routine that is outlined in the thread you referenced. If nothing turns up, and still no code,s then starting pulling spark plugs, check coil packs and wires, injector cleaning additives, yada yada