Loss of RPM’s & rough idle, at start-up

[Texican65]

Hi guys!

My ‘89 Ranger 2.9L w/ 150,000 miles is doing something odd. I drove it around all morning, no problems, let it sit 3 hours, went to pick my kid up from school and….

When I cranked it up, the “check engine” light came on…which I have never seen in 15 years of owning the truck, and the RPM’s just dropped off from a normal 1000 or so to 500.

The truck immediately started running rough and smelled rich. I gave it some gas and the RPM’s climbed, the “check engine light” went away and the truck smoothed out, and stayed that way until i let off the gas. Then RPM’s dropped to 500, light came back on, running rough and smelling rich then died.

Any ideas?

thanks,

Dow

 

[franklin2]

Check for a vacuum line that may have popped off. One to really look at would be the one to the MAP sensor mounted on the pass side inner fender. You could also pull the codes, since you did get a check engine light. That means it did recognized something was wrong and it will store the code as long as you do not take the battery cable off.

 

[Texican65]

Cool…thanks for the help. While looking for the MAP sensor…I found a very small 1/8” line running to the vacuum tree on the left side of the intake manifold…and it was ripped in half. I taped it back together with rescue tape…started the truck up…and she ran just fine. Took her for a test spin…ran just great.
Could that little line really have been the issue?

Thanks!
Dow

 

[bobbywalter]

If it's feeding the map....for sure

Did it back fire or pop recently?

 

[rusty ol ranger]

Cool…thanks for the help. While looking for the MAP sensor…I found a very small 1/8” line running to the vacuum tree on the left side of the intake manifold…and it was ripped in half. I taped it back together with rescue tape…started the truck up…and she ran just fine. Took her for a test spin…ran just great.
Could that little line really have been the issue?

Thanks!
Dow

The MAP relies on vaccum to teLL the ECM what the engine is doing (IE low vaccum means dump fuel, high vaccuum means drop fuel...very simply put lol) if the line to the MAP was busted it would think you needed fuel. The other sensors saying "WTF is going on im already flooding" is why it didnt die tottally.

Yes that line is important i had mine break and do similar.

 

[Texican65]

Hi, thanks for the replies.
No it wasn’t the line to the MAP…
And I took her for a spin again…and same issue.

So…I figured I’d ask the OBD1 what it thought. The numbers I got, if reading it correctly, were 11, 11, 163, 63.

11 apparently means system working…couldn’t find a 163….and 63 is “Throttle Position Sensor”…sooo…hoping that could be the issue. I guess I’ll find a new one and go from there.

Do the symptoms I’m having sound like they could be related to a bad throttle position sensor?

thank you

 

[franklin2]

Hi, thanks for the replies.
No it wasn’t the line to the MAP…
And I took her for a spin again…and same issue.

So…I figured I’d ask the OBD1 what it thought. The numbers I got, if reading it correctly, were 11, 11, 163, 63.

11 apparently means system working…couldn’t find a 163….and 63 is “Throttle Position Sensor”…sooo…hoping that could be the issue. I guess I’ll find a new one and go from there.

Do the symptoms I’m having sound like they could be related to a bad throttle position sensor?

thank you

Each time you mess with the gas pedal it does seem to change how it runs. So it is possible. They do wear out eventually. Also check the wiring and the connector up at the TPS.

The guy in the fuel injection books tells you to unplug the tps connector, take a jumper wire and jump the orange wire to the darkgreen/lightgreen wire. Then do the key on engine off code tests again. With the jumper in place, you should get a code 53. If you do, he says to replace the tps sensor.

He says code 63 means the TPS voltage is low. By jumping the orange wire (5v supply wire) to the darkgreen/lightgreen wire (signal wire to the ECM) that will generate a TPS voltage is high code which is 53. So if you get this code, that means the computer is working, there is 5v at the TPS, and the only thing that could be wrong is a bad sensor.

 

[Texican65]

Each time you mess with the gas pedal it does seem to change how it runs. So it is possible. They do wear out eventually. Also check the wiring and the connector up at the TPS.

The guy in the fuel injection books tells you to unplug the tps connector, take a jumper wire and jump the orange wire to the darkgreen/lightgreen wire. Then do the key on engine off code tests again. With the jumper in place, you should get a code 53. If you do, he says to replace the tps sensor.

He says code 63 means the TPS voltage is low. By jumping the orange wire (5v supply wire) to the darkgreen/lightgreen wire (signal wire to the ECM) that will generate a TPS voltage is high code which is 53. So if you get this code, that means the computer is working, there is 5v at the TPS, and the only thing that could be wrong is a bad sensor.

Thank you very much…I’ll try that and reply how it goes!

 

[Texican65]

Well… I done swapped the TPS out…and so far she’s running like she’s supposed to. No issues like before, hopefully it stays that way.

Thanks again for all the help guys.