Car Rpm drop when slowing down, help?

[jayce]

Hello fellow ford drivers!

this is my first post and i appreciate any help or ideas thrown my way.

i just recently had my car taken in to the shop to change a catylitic converter( both sides & new muffler, direct fit parts NOT magnaflow) , anyway, one of the reasons i took it in was that the car was idling very poorly, and once just shut off, it started right back up and hasnt done it since...however, nearly EVERYTIME i slow down, the RPM gauge dips hard from 6-700 RPM to around 3-500 rpm and the car shutters and you can see the power loss and the straining of the alternator to keep up..and when at that stop, you can feel the engine become sluggish as it sits there for a minute.

ive had multiple converters put on in the last couple years, which indicates an underlying issue( id assume). now, ive recently had a pcv valve fixed, have spark plugs( i assume the right spacing)...
upon start up i can feel hesitation but it starts right up, idling on a small incline, you can feel it being very sluggish..


my main issue is diagnosis, its NOT throwing any engine codes at all, zero. the lights all work but they arent being tripped. could this be a Mass air flow, throttle position sensor or idle sensor?



i do know my POWER STEERING pump is going bad, when fully left or right on the wheel , you can here the strain of it, and when stopped and turning wheel, you can feel and see a power dip that is similar to the rpm drops i experience when driving( when driving i do not move wheel left or right when slowing down, so im not sure if this is a possible culprit or just a separate issue)


vehicle is:

2000 ford expedition XLT 4.6L A4wd

 

[1955moose]

I guess my first question is why did you have the catalytic converters changed? Was that the diagnosis of a shop somewhere. Having a jumpy idle can be numerous things. Usually the first is to run diagnostic codes, but you state their aren't any. Zero. Well next two things I would do if it were my SUV is have the fuel pressure checked, and second have a shop do a smoke test on intake/ Exaust for leaks. Particularly intake leaks. Your jumpy idle sounds like a vacuum leak somewhere in the system. Hose, gasket, etc. You also state the straining of alternator to keep up. I would have your battery load tested, be sure cables are clean/ tight, and be sure alternator is charging properly. Let us know what you find.


Sent from my iPhone using Tapatalk

 

[docraymund]

Jumpy idle when slowing down indicates a vacuum leak. Rent a smoke machine to rule this out. Another cause would be a worn brake booster allowing more air to flow when you step on the brakes. Search the web on how to test this. Also, your power steering reservoir may be low on fluid.

 

[jayce]

I guess my first question is why did you have the catalytic converters changed? Was that the diagnosis of a shop somewhere. Having a jumpy idle can be numerous things. Usually the first is to run diagnostic codes, but you state their aren't any. Zero. Well next two things I would do if it were my SUV is have the fuel pressure checked, and second have a shop do a smoke test on intake/ Exaust for leaks. Particularly intake leaks. Your jumpy idle sounds like a vacuum leak somewhere in the system. Hose, gasket, etc. You also state the straining of alternator to keep up. I would have your battery load tested, be sure cables are clean/ tight, and be sure alternator is charging properly. Let us know what you find.


Sent from my iPhone using Tapatalk

The innards were rattling around really bad. They needed changed..and I believe they keep needing changed due to an underlying issue causing then to fail faster( just an semi educated guess).

My throttle isnt jumpy at all,
When pressing brake coming to a stop in my expedition, My rpms dip to under 500 and as a result the car struggles to stay on..and jumps back up to normal , it causes a hesitation..a shuttering ..
My main thoughts were it's not throwing no lights or codes, zero..the shop said the previous shop erased codes and none were throwing for them when they were replacing converters.

My thoughts were either it was weak alternator( but no codes are being thrown....do codes pop out for alternators?), bad mass air flow sensor, or Intake area dirty...


Here's a secondary question:

Can I buy a volt meter and test voltage to alternator to see if it's running proper without removal?

And I think I can test the mass air flow sensor with the volt meter..

 

[jayce]

Jumpy idle when slowing down indicates a vacuum leak. Rent a smoke machine to rule this out. Another cause would be a worn brake booster allowing more air to flow when you step on the brakes. Search the web on how to test this. Also, your power steering reservoir may be low on fluid.

 

[jayce]

Wouldn't say jumpy, unless you mean dips down then back up...only when slowing down to a stop at 10-15mph or less.
And assuming it could be vacuum issue, are there common things to start looking at first over others? I figure I'd check hoses for cave ins or tears and idk after that lol..
I'm no mechanic, so I'm doing my best to avoid more costs.

I paid 1,426 for 4 converters/muffler last week.

 

[intelisevil]

I had similar idle issues with my Explorer. I even had to shift to neutral and keep my foot on the throttle to keep it from dying at a stop light.

In my case cleaning the IAC valve cured my problem. About $5 for a can of contact cleaner and 15 minutes under the hood.

 

[Bedrck47]

You have the 4.6 Have you ever removed the throttle body and cleaned the exhaust ports thru the TB. Very good video on youtube about this. Also check the hoses going to the DPFE sensor.

 

[1955moose]

Early or multiple time catalytic converter replacement is usually due to an over rich running condition. You need to get a handle on what's causing this A.S.A.P. I apologize, I didn't fully read your post properly, and was giving advice more on symptoms, rather than what was actually going on. You can try diagnosing your intake leak, if you have one, by either spraying down each gasket, hose, and joint with a can of carburetor cleaner, or equivalent spray. I like using Wd 40, then wiping everything down afterwards. This process is very time consuming in comparison to smoking the intake with a machine. Bedrck had a good idea about cleaning out port on throttle body. You can do that job. You may also want to be sure your Egr is functioning properly, including the port that runs through it. How are the brakes working, in particular does it slow down with the assist of the booster, or do you have to mash hard on pedal? As to your question you can buy a inexpensive voltage tester for $20.00 to do voltage and ohm tests. You can check voltage output of your alternator either by using voltmeter directly at battery terminals, or by putting red lead of meter at post of alternator and black to battery ground. The reason I suggested battery/ alternator test is to see if you have a failing battery, or alternator voltage/amperage output. Auto zone or Oreillys does it for free. Now you have a few things to repair and a few to check. Keep in touch how it turns out.


Sent from my iPhone using Tapatalk

 

[Erlejames]

I have a 99 expedition with a 4.6L. Same problem. I found that the PVC hose had burnt through the rubber adjacent to the valve. Snipped the burnt end off and all is good.

 

[UtilityCow]

Dealt with a similar problem recently.
Checked all the common vacuum hose problems.
Replaced IACV and cured. Use only a Motorcraft valve and purchase on Amazon. They're cheap. I've replaced a lot of these on my Fords over the years.

 

[jayce]

I have a 99 expedition with a 4.6L. Same problem. I found that the PVC hose had burnt through the rubber adjacent to the valve. Snipped the burnt end off and all is good.

I'll inspect the hoses more. I believe it's a sensor dying out more than anything..but won't rule out any ideas.

 

[1955moose]

The Beauty of the forum is you get various solutions and tests, that other forum members found fixed their similar problem. Start at the basic/cheapest first, and advance from there. Always do your own diagnostic with Dtc codes, and fuel pressure tests first. Keep us posted what you find, helps others! Moose.


Sent from my iPhone using Tapatalk

 

[jayce]

The Beauty of the forum is you get various solutions and tests, that other forum members found fixed their similar problem. Start at the basic/cheapest first, and advance from there. Always do your own diagnostic with Dtc codes, and fuel pressure tests first. Keep us posted what you find, helps others! Moose.


Sent from my iPhone using Tapatalk

I'm gonna start with replacing mass air flow /IAC/tps and go from there, and inspect hoses.
I'm no mechanic so I'll get my buddy to wrench em on. I do kinda get how all these parts fit and work with each other, I've just never wrenched em off or on before.

 

[1955moose]

It's not that hard to diagnose your vehicle. Sure wish you wouldn't just throw parts at it. I've seen too many of members do that, and $1,000 later, they still haven't fixed problem. If your not mechanical and want to save a few $ have a reasonable shop diagnose your problem, then replace that part. The Tps switch in particular is a pain in the &&@ to change. The screws strip or break. It's your car, you asked for help, please use it wisely.


Sent from my iPhone using Tapatalk

 

[UtilityCow]

The Beauty of the forum is you get various solutions and tests, that other forum members found fixed their similar problem. Start at the basic/cheapest first, and advance from there. Always do your own diagnostic with Dtc codes, and fuel pressure tests first. Keep us posted what you find, helps others! Moose.


Sent from my iPhone using Tapatalk

I saw a lot of solutions to my problem. No bad hoses. Tested fuel pressure and replaced fuel pump. Didn't fix it. Replaced aftermarket IACV and cured. Love forums.

You can test the TPS with a multimeter. 5 volts at WOT I believe.

 

[1955moose]

Yep that's about what wot voltage is. Should start at 0.6 to 1.1 I believe, and should be smooth all the way to 4.5-5.0 volts. A bad one is jumpy when accelerating with motor off, and volt meter connected. They must put on red lock tight on screws, cause I heard their a bear to remove. I've changed tps switches on 5.0 Fords that were easy. Go figure, they never make anything easy on these SUVs.


Sent from my iPhone using Tapatalk

 

[jayce]

It's not that hard to diagnose your vehicle. Sure wish you wouldn't just throw parts at it. I've seen too many of members do that, and $1,000 later, they still haven't fixed problem. If your not mechanical and want to save a few $ have a reasonable shop diagnose your problem, then replace that part. The Tps switch in particular is a pain in the &&@ to change. The screws strip or break. It's your car, you asked for help, please use it wisely.


Sent from my iPhone using Tapatalk

From the way it drives, what I've heard here and advice from my friends who are Mechanics, I've leaned towards being faulty sensors...that doesn't mean I'm ruling anything out. Mad/IAC/tps arent that pricey, the shop fee here us 85-115$ an hour. Plus they have to diagnose it first..which could take a long time considering no engine codes are throwing...I've put so much money in this vehicle by putting it in shops this whole.time and I don't have any money or a better car to show for it lol.

 

[1955moose]

I understand. Keep us in the loop, maybe we can help.


Sent from my iPhone using Tapatalk