My s10 has the 4.3L v6 and lately it has begun to start hard, particularly first thing in the morning. I have replaced an o2 sensor and now have no CELs. I can get it to start by holding the accelerator down just a bit while turning the key. After it is warm it seems to start ok. But may have a little bit of a mis while driving, until it warms compeltely. Not sure... very small mis if any, but something feels a bit off until fully warm. I am thinking TPS or IAC, though I have removed and cleaned both with no results. Any help would be appreciated. I also have a new fuel filter and hate to think about it, but have also suspected a fuel pump issue.

Thanks in advance for any help.

My first thought would be the IAC also. You may have to take the TB off the intake manifold and completely clean it especially where the IAC pintle seals against the TB.

I have also been reading similar symptoms with a bad fuel filter. I have one and its due so that will be next I guess, then the IAC and TPS. No lights so that too would seem to suggest fuel filter.
If I give it just a smidge of throttle it will start right up... its starting to mis more and more too. Again, FF seems likely.

No, absolutely nothing suggests fuel filter.

Cracking the throttle open SUGGESTS that the IAC isn't opening all the way during a cold start.

Do you even have a clue what the IAC does?

Make sure the pintle is clean, the mating surface is clean, as well as the passageway......and also make sure the throttle plate AND bore is clean......

Wouldn't hurt to replace that fuel filter......also check fuel pressure if you have a gage....

Would also clean the MAF sensor element with MAF cleaner and makes sure there are no air leaks going into the throttle body after the MAF.....

If it runs normally when warmed up then I tend to agree with the guys above that it'* not a fuel filter causing this issue. Minimal fuel flow at idle that is hindered by a bad fuel filter would make it barely run at all when warmed up.

I also agree that if it is due for a filter due to time or mileage, no harm in replacing.

I agree that IAC seems most likely. Even a clean one can function improperly.

How many miles on this car?

How many miles on the current set of spark plugs?

How many miles on the wires?

In which part of the world does this car live?

205,000 miles, In Michigan, plugs and wire have about 60k on them and seem to be in good condition. Since my last post, I pulled the cap and cleaned it and rotor. They were very corroded and I was sure I had found the problem.. but although it is not missing when driving warm now, it still has the hard start problem. Have not been able to decide if its a COLD start / Cold temperature problem or possibly something else affected due to sitting for extended periods. (overnight)

I did also get a pressure gauge on it and it reads about 60psi with ignition on and 50psi while cranking over. According to what I have read, 50 is minimum needed and if so, I must need a pump? What number should I have with healthy pump? I have read where some have referred to the replacement as an "easy and inexpensive" fix.. Well, I am not cutting my bed but would lift/remove it for the fix and I have gotten a price of over 400 dollars for the pump. Not too cheap. I can get a rebuild kit for something like 50 dollars, but am unsure as to how well that would work/ quality of the rebuild parts etc. The main seal for example, looks very different in the kits than the original. I am replacing the filter as I know it is due/old and do wonder if the pressure would be that much effected by a dirty filter. Guess I will find out. I will also likely replace the IAC as it is original to the best of my knowledge. I have cleaned MAF senor wires with cleaner made for that job. There was a hole in the cold air intake tube a while back but has been patched. Could be leaking but would have to be a very small leak... I plan to replace the bad tube and have it ordered now. My air filter was replaced last summer but it was an ebay special and it has crossed my mind that it may need replacement. Will test that. As of now,,, if it has been running. It will start and run fine. It is cold here now, very cold and this morning it would not start until I cranked it continuously and depressed the pedal. Once it runs it runs and starts fine.... Cannot work out in my mind, why a failing pump would cause this unless the running engine / spinning alternator give the pump a boost and that makes the difference in pressure. Anyway.... back to the salt mine.

You said you pulled the TPS out, why?

You said, the engine will start ONLY if you depress the accelerator a little bit to get it started. This has nothing to do with fuel pressure. THIS has everything to do with AIR getting into the engine. This is a common problem with FI engines that are controlled by an IAC. Your accelerator does not control fuel pressure. It only opens the gate for air to flow more or not, it also tells the PCM at what % the throttle is open. The PCM does not control fuel pressure. Its either on or off. IMO, to eliminate the IAC as a culprit, replace it and remove the TB and clean it top to bottom. Then retest.

Let'* change lanes.... you have the original poppet injectors do you not? They have been known to fail(just enough) to cause fuel to leak out when they are just sitting there. Your engine could be 'flooding' itself while it sits over night. These older poppet injectors have been known to cause hard starts also. One way to find out is to park the vehicle over night, go out the next morning, pull the intake pipe off the TB, open the throttle all the way and stick your nose inside. Does it smell like raw fuel? If it does, your poppets are leaking and you need to replace the entire spider assy. Do not use the same style. They have an upgraded kit that fixes this. A tad more expensive, but worth it in the long run. People have commented that the engine runs smoother after the upgrade(it is an OEM upgrade)

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