I seem to have a small hesitation problem when starting the car cold. The car will start and idle fine but if I rev it up right away it hesitates until it gets past around 2500rpm and I can smell some unburned fuel coming out of the exhaust. This only happens if I haven't driven the car for five or six hours but the car runs with no issues once it is warm and will start rigth up and won't hesitate. It has also done this a few times in the morning when I turned the car on and put it in drive within 30 seconds. I have replaced the cap, rotor, wires, spark plugs, ignition coil, seafoamed the intake twice within the last month ( which fixed a low idle issue I had) and I have ran 6oz of acetone in the tank for one full tank and a half can of seafoam on the last tank. I have also checked each spark plug wire with an inductive engine analyser and they all have a steady spark going through them. I don't think it's the injectors since it only does it when it's cold. At first I though it might be the cold start valve but now I think that if it was the cold start valve then the car would just take longer to start but I don't think a faulty valve would cause hesitation or would it? any ideas?

Thanks

 

I forgot to mention I have also replaced the flame trap, nipple and flame trap hose...

 

Not sure about newer 240s, but for the old ones, two typical faults could be the cold start injector and the thermal time switch. The latter is expensive for a new one, but a junkyard one could be cheap.

 

Thanks. That is something I was a little confused about. The Haynes manual refers to three temperature sensors. One is the gauge temp sensor with one wire, which I know it just feed info to the gauge. It also refers to the Thermo Time switch that feeds into the cold start valve and in another section it talks about the coolant temperature sensor (two wire one) that feeds info to the fuel injection system. I looked all around the engine block and only found two temperature sensors so I'm guessing the thermo time swith and the fuel injection temp sensor are the same thing? is that correct? If so, iPd sells it for only $22.69 but I'm not looking forward to having to change it cause it's burried under the intake manifold and there is very little access to it. From reading the manual it seems that the thermo time switch was replaced with the fuel injection temp sensor in the newer 240s but I'm not sure cause the manual sucks and doesn't specify. It shows the thermo time switch with one wire going to the starter and the other going directly to the cold start valve so I guess it makes the cold start valve spray fuel only while the engine is cranking..... if that's the case then I don't think that is my problem cause the engine starts fine but hesitates if I rev it up right away or within a minute of being started....

 

No thermo time switch on a 91. The two wire temp sensor should be measured to ground, resistance wise, before you replace it.

 

Will do. Thanks

 

Fixed!!! What a relief!

I wanted to upgrade my plugs since I changed my ignition coil to the Accel performance coil a while back so I decided to try the E3 spark plugs (http://www.e3sparkplugs.com/). Man, these things cured my hesitation and the backfire I was hearing coming from the intake. I don't even smell gas out the pipe when I start the car cold like it used to. The other plugs I was using only had 8k miles on them but they were Bosh.... I'm sticking to E3s from now on... I'm SOLD. These plugs are amazing... I can even feel a little more pull and it revs up quicker than before... They cost a little more ($6.99 from Checker) but I think they are worth it. I would highly recomend these...

Has anybody else tried these plugs?

 

I have and had the same issues with my car and the same result. I would also recommend these plugs.

 

I'd love to give these E3's a try, but I can't seem to find which ones are the right ones for a 240. Their website doesn't seem to list info for the 240 anywhere, and Amazon search comes up short, too.