Hard to Start again after warm up

The IAC was clean like new and moves smoothly with no binding. Checked for vacuum leaks, none found. Still starts great on cold first start, but after that, its still hard to start.

Hi everyone! It's been a very long time since I've been on the site, glad to be back. Got a new home, kids off to college in a few weeks and my Bird just sits in the garage waiting for me to take her for a walk again. I am re-entering this post that I reached out to many of you back in 2011 and to date, I still have the same problem during the starting process. When engine is cold, it starts up right away. When warmed up and you shut 'er down, then try to start it back up warm or hot, she lags to light off and in most cases, I have to move the accelerator all the way to the floor and hold it there for a short moment until it starts. I had many replies to help with this problem back then and finally figured out what is going on, so at least I hope.

I was able to successfully run the codes and got KOEO 51, KOER 21. This ECT sensor lives under the air intake between the injectors based on the diagrams, no fun getting to it. From what I understand and taught myself, that this sensor reads the coolant temperature and changes how the air/fuel is mixed together. What I have figured out, when the engine gets warm, this sensor tells the computer the engine is warm, so as not to put as much fuel into the cyl's when warm. If this sensor isn't working, the computer thinks the engine is cold, therefore, puts too much fuel in the engine during a warm start up, causing a lag during the start cycle or hard to start.

I replaced the sensor and still have the same codes, which now leads me to wiring. I reach out to you guys again to see if anybody else has had this problem? if so, where are the common known places to find wiring issues with this sensor? I know someone will say check the plug first, which I will, but where are the next places to find a wiring problem with this sensor? With this sensor not working correctly, may explain why my engine runs perfectly smooth when cold, then has a very minor miss once it's warmed up. I suspect that the computer thinks the engine is cold, therefore, puts more fuel in the engine when warm, causing this miss to happen, or a minor rich condition.

For those who care, I had her painted last summer, unfortunately, not with the same original twilight blue. I got tired of the original and went with a Mercedes blue 890, one because it looks unbelievable and two, you would all die to find out what I paid a professional to do the job, so I kinda had to go with this to keep costs down. Put new wheels on and they look great as well, never did like the snow flake style from day one. I've had more people say WOW, where did I get this car at. I've had more compliments on the color and wheels than I ever did with the original color and wheels. I love my car, never will let it go and the first owner. Now it's time for the interior. I would love to show pictures, but not sure how to do that on this site.

Thanks again for listening and helping out with this sensor issue. Note: I took the removed old sensor and checked the resistance cold, it reads around 32-34 ohms. When I put sensor into hot water, the resistance changed to around 5-7 ohms, which tells me the sensor seems to be working fine. Not sure what the values are, but since I still have the same codes on the new one, I assume these values are possibly normal. Now, where is the common wiring problems with this?? Thanks guys

See "Eng Colnt Sen" along the top and ECT at pin 7 (left side) Check it from the connector back to the EEC which is behind the footwell cover on the passenger side.

Thank you much Pete for the diagram, this will be a big help to try and locate this problem. Take care, I'll update with results

Are you sure you are reading the resistance of the sensor correctly? Cold the resistance should by 30,000+ ohms and at 200 or so degrees it should be a few thousand ohms.

The ECT circuit goes thru the same connector that the injector circuits go thru. The connector is located near the rear if the intake, roughly above the pulse damper. Check it to be sure it is tight, no corrosion, etc.

Hey Jeff and Pete. I've got good news!! Thanks for the wiring diagram, it was a huge help. I checked the wire green/yellow from the ECT plug to pin 7 at the computer, all checked good. When I checked the ground wire at the ECT plug to pin 46 at the computer, I have nothing at all. After looking over the wiring diagram, the ground is shared with the knock sensor and the air charge sensor. From there it goes to another junction to tie other grounds together as well. When I checked the knock sensor ground at the plug, I also didn't have anything to pin 46. I checked the ground at the throttle pos sensor to pin 46 and the self test connector plug to pin 46 and they checked good.

I made a dummy jumper wire and back probed it to the knock sensor plug ground, it gave me a good ground to the air charge and ECT plug. This knock sensor plug was the easiest plug to get to. Took the car for a drive to get it good and warm and she now starts up immediately after shut down, no more pushing the pedal to the floor to get it started. YEAH!!!

My question is now, will it be ok to hard wire a ground wire to the knock sensor plug to vehicle ground, being that I do not know where the the break is in the wire going from the three sensors. These three sensors (air charge, ECT and knock sensor) are tied together at a junction per the diagram now have a ground. The broken wire is somewhere between that junction and the next ground junction that ties the other things I mentioned.

I could run a jumper wire from the knock sensor to the wiring harness on the back side of the intake which is right next to the knock sensor plug which has the black/white ground wire going to pin 46 at the computer. I don't know if the computer has control over this ground for the ECT or any good ground will do? If any good ground will do, I will hard wire a ground from the knock sensor to vehicle ground. The big question is, should I tie these three sensor grounds to the black/white wire going to pin 46 at the computer?

Any thoughts? Again, I appreciate all this help. I've been scratching my head for several years with this problem going after everything else.

ALL sensor grounds MUST be returned to SIG RETURN, at pin 46. SIG RETURN and "ground", such as the engine block, frame,etc, are NOT the same!

Thanks Jeff, good information to know. I will make to proper connection this weekend. Thanks again for the help