Rough idle on cold start

[Kami808]

It got worse and worse hopefully someone here had this familiar issue that could help me.
I'm trying to fix this rough cold start issue, low engine RPM-500 it will do it again on the next day when engine is cold once engine warms up it goes back to normal RPM-1000.
First thing first I tested my engine coolant temperature and air intake temperature with a multimeter ohms reading are nowhere close to volts reading also on the negative ohm reading if I switch my wires around will get no reading at all. :scratch:
also no codes and these sensors were replaced about 7 months ago.

Some things I have done
disconected the ECT when engine is cold its crazy no rough idle and no engine jumping around rpm stay about to 1000.
I still have my old sensors plugged them in read same reading and same issue.

Here are my readings
(82°F)
[ECT]
Volts: 2.95
Ohm:
20k: -6.86
200k: -40.2
[IAT]
Volts: 2.72
Ohm:
20k: -7.01
200k: -40.1

A helpful chart I found in the forums

any help is much appreciated

 

[Kami808]

Today I did more test to the ECT sensor I took the sensor out to test its Ohm resistance placed on hot water resistance slowly drops I think its reading ok, then I placed the sensor back on connected warmed up the engine ECT sensor resistance stay about the same as cold and volts were slowly dropping as its get warmer.
I could also try buy a new ECT sensor.

 

[tonytheexplorer]

Have you checked your spark plugs?

 

[malohnes]

Sounds more like a faulty IAC to me... I'd clean your MAF, check the TPS and IAC. Also check for codes. Oh, and try resetting the CPU by disconnecting battery power for 15-20 minutes if your component checking and code reading comes up clean.

 

[MrShorty]

Here are my readings
(82°F)
[ECT]
Volts: 2.95
Ohm:
20k: -6.86
200k: -40.2
[IAT]
Volts: 2.72
Ohm:
20k: -7.01
200k: -40.1

This looks to me like some kind of user error. The volts readings look normal and right in line with expected, but those resistance readings look like you are missing something when testing resistance (like, is the sensor still connected to the PCM and power turned on while reading resistance).

Assuming some kind of user error while reading resistance, these temperature sensors look okay to me.
I would second cleaning the IAC and intake. I would probably also test fuel pressure cold to see if it is taking longer than usual for adequate pressure to build up.

 

[2stroke]

Also I should state that 1000 rpm is not the normal idle speed. 650 rpm is idle, and its possible you have a vacuum leak, maybe having to do with the thermostatic control valve?

 

[Kami808]

Sorry for my delay
Thanks guys for the help I have finally found my issue there was a vacuum leak in the intake manifold bad gasket and the pcv valve was not working properly.

 

[Kami808]

Fixed and more problems!!

I'm back I have fixed my idle problem when cold start replaced 4 gasket and the PCV valve it start fine no problem now another problem comes in when its warmed up the idle goes up and down ill say to 900 to 700 fuel pressure is at 35psi, also got a code 41 System too lean I can't think of anything else what is causing this maybe you guys do.
most parts where replaced not too long ago and almost not too much driving.
I cleaned the MAF And IAC no change and resetting computer.
maybe injectors?

Video:
I know my fuel is on low recently put fresh gas in.
https://www.youtube.com/watch?v=97weNsE0ImY

 

[OneofMany]

Does a 91 have EGR?

 

[Kami808]

Does a 91 have EGR?

No EGR on a 91.

 

[OneofMany]

Check for vacuum leaks.

 

[Bmoresports]

poor engine preformance

My 94 explorer has not been preforming on the level it has in previous months. The engine runs poorly while cold and idling especially. Its lost some power for sure and only has 133000 on it. While driving on the highway i can hear a noticeable rattling coming from the engine although it could be one of the cats. Ive done the radiator, spark plugs, coil, fuel pump, fuel filter, thermostat and ive cleaned the MAF.
Could it be one of the oxygen sensors? i dont have a check engine light so maybe not. Possibly injectors? Im somehow under the impression that's its a sensor of some sort but its pissing me off really bad because i love this car but its driving like crap.

If anyone could tell me what needs to be replaced around this millage and what it could be from my description that would be so helpful because i cant find solid answers anywhere right now.

 

[Rhett]

I'm back I have fixed my idle problem when cold start replaced 4 gasket and the PCV valve it start fine no problem now another problem comes in when its warmed up the idle goes up and down ill say to 900 to 700 fuel pressure is at 35psi, also got a code 41 System too lean I can't think of anything else what is causing this maybe you guys do.
most parts where replaced not too long ago and almost not too much driving.
I cleaned the MAF And IAC no change and resetting computer.
maybe injectors?

Video:
I know my fuel is on low recently put fresh gas in.
https://www.youtube.com/watch?v=97weNsE0ImY

I know you cleaned the IAC, but it may be the issue. It may not be working properly. Have you also made sure the TPS voltage is all right?

 

[Rhett]

My 94 explorer has not been preforming on the level it has in previous months. The engine runs poorly while cold and idling especially. Its lost some power for sure and only has 133000 on it. While driving on the highway i can hear a noticeable rattling coming from the engine although it could be one of the cats. Ive done the radiator, spark plugs, coil, fuel pump, fuel filter, thermostat and ive cleaned the MAF.
Could it be one of the oxygen sensors? i dont have a check engine light so maybe not. Possibly injectors? Im somehow under the impression that's its a sensor of some sort but its pissing me off really bad because i love this car but its driving like crap.

If anyone could tell me what needs to be replaced around this millage and what it could be from my description that would be so helpful because i cant find solid answers anywhere right now.

What kind of gas mileage are you getting?

 

[Kami808]

Check for vacuum leaks.

I'm sure I don't have any more vacuum leaks I checked for lines and don't hear any air getting into

I know you cleaned the IAC, but it may be the issue. It may not be working properly. Have you also made sure the TPS voltage is all right?

It could be the IAC and Yes TPS voltage is ok.

 

[OneofMany]

The problem occurs when the engine goes into closed loop. Check your O2 sensors.

 

[Bmoresports]

I know you cleaned the IAC, but it may be the issue. It may not be working properly. Have you also made sure the TPS voltage is all right?

My millage is alright but has gotten slightly worse ever since the performance drop and rattling sound.

 

[OneofMany]

Find the rattling.... Maybe a stethoscope will be helpful at pinpointing it.