Bad MAP Sensor?

Edgar Marton

Edgar Marton

Member
Joined
Aug 20, 2019
Messages
40
Location
Budapest
Hi guys, Another little problem, hopefully you can help. Jeep runs well when it runs. When starting it runs very rough (15 seconds, revs start at 500 and slowly work their way up to 1000 rpm and then stay constant) - looks like the engine is not getting the right mixture to start.
Throttle body already cleaned 1000x.
IAC also already cleaned.
MAP sensor?
Best Regards from Hungary
Edgar
 
I'll take a measurement in the evening - I've read that 40 psi is normal - how high should the value be at the start?
Thanks for the help Mac - in Ungan we are only 10 Jeeps and where I live I am the only Jeep in a radius of 200 km - so I can't ask anyone here. There is another forum in Germany - but the guys there are unfriendly, not very helpful and more concerned with showing tuned Jeeps than with technical problems.
 
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A steady 40 would be fine. I believe technically it's supposed to be 43. Mine is running on 35...that or my 20 yr old OTC gauge isn't accurate.

-Mac
 
Edgar Marton said:
approx. 40 psi, no engine light / ecu error code
Click to expand...

I wouldn't focus on the map sensor per se. The issue is crappy/low idle at start. Work that problem. Does it have the same behavior from a hot start as a cold start? Just because your IAC is clean doesn't mean it's working. How does the Jeep run after the initial low idle? Does it drive okay?
 
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Torque:
Idle - TPS 16.9 % / Vacuum: 18,4

photo_2024-03-07_21-08-18.jpg


no idle, only Ignition ON
TPS 16.9 %
shouldn't the value be 0 % ?
Perhaps the TPS is faulty?
Can I clean it?

photo_2024-03-07_21-08-12.jpg
 
Edgar Marton said:
Torque:
Idle - TPS 16.9 % / Vacuum: 18,4

View attachment 507468

no idle, only Ignition ON
TPS 16.9 %
shouldn't the value be 0 % ?
Perhaps the TPS is faulty?
Can I clean it?

View attachment 507469
Click to expand...
Can you clean a TPS? Yes. But not the part that fails. The TPS is a potentiometer, and all that is is a band of plates that increase or decrease resistance and report that R value to the PCM as you move the pedal. That's inside the sensor, and it is attached exterior to the throttle body. It doesn't come in contact with air or fuel like an IAC valve, O2 sensor, MAP sensor, ETC. It doesn't get dirty. It fails, your symptoms are more in the IAC circuit. A clean IAC valve doesn't mean it's an operational IAC valve.

Just like the MAP sensor, back probe the signal wire and ground your voltmeter. Move the pedal lock to lock looking for dead spots in the voltage range. While the car is running, if the RPM's don't fluctuate or you don't get any stuttering it's likely not the TPS.
 
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I can try to describe the problem again. I start normally (starter motor starts immediately) and the engine speed increases slowly from approx. 500 rpm to 1200 (in approx. 3-4 seconds and then remains constant at 800 rpm. It looks like the engine is not getting enough air, fuel or "love" in the first few seconds. Unfortunately, I can't describe it any better than that. I have the feeling that the engine "sags" in the first few seconds, then it catches up and runs normally.
Thank you for your help - you are the best!
Greatings from Budapest
 
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You never answered my question on how it runs after this initial idle issue. And if you think you are having trouble accurately describing what's going on, I suggest posting a YouTube video of it.

Do you plan to attempt any of the troubleshooting suggestions? Do you have easy access to parts? A TPS and IAC are cheap enough over here to just swap out and check.
 
SkylinesSuck said:
You never answered my question on how it runs after this initial idle issue. And if you think you are having trouble accurately describing what's going on, I suggest posting a YouTube video of it.

Do you plan to attempt any of the troubleshooting suggestions? Do you have easy access to parts? A TPS and IAC are cheap enough over here to just swap out and check.
Click to expand...

Hello SkylinesS., Sorry, I don't understand the question. I have written several times that the engine runs normally and idles at approx. 800 rpm.
No, I don't have easy access to spare parts but have to order everything expensively from Rockauto. The spare parts are cheap, but the shipping costs plus tax are often three times the value of the spare parts. Driving an American car in Europe is ok - but only if there is a spare part store nearby. I am only driven by my passion for American cars (and that's why I've been ordering from rockauto for many years) - otherwise I would have sold the Jeep long ago. Be happy to live in a car country - here in Europe bikes and those damn bike lanes everywhere are more important than cars. Greenwashing politics everywhere - no fun to drive in Europe and especially to repair a car.
 
Edgar Marton said:
No, I don't have easy access to spare parts but have to order everything expensively from Rockauto. The spare parts are cheap, but the shipping costs plus tax are often three times the value of the spare parts.
Click to expand...

Need an American friend on a military base or FOB with an APO.

In the good old days we'd order snack food on Amazon and send it to Afghanistan.

-Mac
 
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