My 1998 ram van (5.2L) has always had this issue from day one since I bought it last year. It shifts and drives like it should I guess, gas mileage is normal, and I put lots of miles on it (I use it to travel, and its done everything from cross country, to the 17,000’ mountains of CO). However, I need to get to the bottom of what this is below. I’ll give two examples of the issues. One will be when the engine starts up an idles, but I don’t drive it right away. And the second one will be if I start it up and drive it right away.

1) So I start the engine up and it seems normal. After about 30-60seconds, I hear (I don’t have a Tach gauge) the RPM’s drop slowly, and the engine/van starts to shake very noticeably. I can hear the IAC (which I already replaced) hissing loudly to try to compensate and keep the engine running. Anyway, the RPM’s keep dropping and van shaking until I tap the gas pedal very slightly, and then the RPM’s shoot way up to what sounds like 1,300-2,000RPMS for about 2seconds, then drop down to a normal idle as it should be. Everything is fine for about 5-10seconds after this, but then it starts doing the above process again until I touch the gas pedal. I need to do this about 3-4x over the course of 3mins. After that, its fine and will run normal for however long you keep the engine on. If it sits longer than 15-30mins turned off again, expect it to do this again. NOTE: Ive never let the RPM’s drop until it stalls, because I didn’t know if it would damage something. Infact, I don’t even know if it will stall? One time I forgot to hit the gas pedal and I think it idled all the way down to what sounded like 100-200rpm’s (barely on), but I quickly turned the key off.



2) Okay so as opposed to above, lets say I start it up and just drive away instead of waiting for the above to happen first. So sometimes, rarely, I can drive off with no issues. However most of the time heres what happens: I start driving and after alittle bit I all of a sudden have no acceleration at all. If I keep my foot on the gas and try to force it, I sometimes hear what sounds like a small explosion or a pop or something. Sounds like its near the CAT area? idk.. I cant tell really. I never force this though because again I don’t want to damage anything. What I end up doing in these cases is just taking my foot off the gas for a split second and pressing again. If it does the same thing with not allowing me to accelerate, I keep repeating a few times until it gets back to normal and I can accelerate. Obviously this isn’t safe if im pulling out onto the road and need to speed up, so I kind of need to figure this out sooner than later.



Idk if its some kind of sensor related? Check engine light goes on and off. Sometimes it remains for weeks, sometimes its gone for weeks lol. I forget the original code, but it was for a water temp sensor if I recall? I replaced that sensor and made sure the connector was securely attached. Anyway idk. Thoughts?

 

Are you still getting the code for the temp sensor? How old is your O2 sensor?

 

Also, does this happen mainly when the engine is cold and never when it's only turned off for a couple of minutes ? What does the temp gauge show ?

Ideally use an OBDII reader with live data and see what engine and intake temps are reading, as well as the O2 sensors.

 

The CEL comes and goes. At the moment, no it doesnt show anything. Sometimes after the issues above, the CEL randomly comes back on and stays there. O2 sensors i was about to replace, but they are stuck. I'll get them off eventually, but yes that is on my list right now

 

Yes it needs to "cool" down a bit first. And then a true cold start it always does it. Temp gauge never goes past the middle. Thermostat was replaced a bit ago with no change in operation. Yes i got a reader, so once i figure out how to use it, i will try to get some data. When the CEL was on, Autozone did their reader and thats how i got the code for the water temp sensor if i recall

 

Hmm, one of the temperature sensors might be throwing the fuel calculation off. That's why it would be good to know what temps the PCM is reading and also what the the O2 sensors see because that will tell if it's a too lean or too rich condition.

 

I recall when first buying it, i saw that the connector to the water temp sensor wasnt connected properly (it was like the wrong connector almost, and it wasnt even making contact with the sensor pins). So i replaced the connector and the sensor, but no change. Do you know how to read the voltage on that connector? It should be pretty low voltage. I just dont know what it should show, or when i should test it (while its plugged in and splice into the wires, unplug it..etc). Note: After 5seconds or so when starting the vehicle from cold start, you can hear the fan engage loudly. Not sure if this is normal, but i do know its related to temp stuff like the temp sensor. EDIT: I think i found some good info on how to check that stuff i just asked about. In the article they said its normal for the fan to kick in? https://www.backyardmechanic.org/how...rature-sensor/

I did buy a MS VC 300 OBD2 reader, but i cant get it to work. I tried numerous ways but it doesnt want to work. Tried on a 1998 and 2002 with no luck. It doesnt appear broken, and i looked on youtube and did what other people did, and still cant seem to get it to give me data (starts to load, then restarts and goes back to the main menu)

 

From what I can tell the reader is a very basic code reader and can not show actual engine data while the engine is running. Both the intake air temp and the coolant temp sensor are just resistors and the PCM reads resistance to ground. Most sensors operate on 5V so I'd think that's true for the temp sensors as well but it's not spelled out in the service manual. You can check the temp sensors by measuring resistance when disconnected, see table below.

 

Yeah i dont think so either. The reader shows alot but not live data like temp stuff. What kind of reader are we talking about and what cost would that be?

I'll test the sensor and the connector again and let you know my results. In the article it says i can disconnect it to test the connector for the 5volts, but i thought it had to be plugged into the sensor to complete the circuit? I recall on my motorcycle i had no voltage in either connector wire unless the connector was plugged into the coolant temp sensor if i recall right

 

Nowadays I'd recommend a bluetooth OBD2 adapter with software for your phone. Most adapters are ELM327 based and dirt cheap, just make sure they work with Apple iPhones if you happen to have that. The beauty of bluetooth adapters is that you can use them with different software application on phones/tablets and/or laptops. There are some other more expensive BT adapters (OBDLink) which can do more than just simple reading from the PCM and control functions of the vehicle but they are of no use for older vehicles because nobody makes software that supports 20+ year old vehicles.

If you don't want to go the BT route $40-$50 gets a you basic OBD2 reader with live data. If you want graphs it's gonna be more, that's one thing you pretty much get with any phone app.

Note that none of these options will allow you to talk to ABS modules on old Chrysler vehicles regardless of what it says on the box because that requires access to a different bus system.