Wants to cut off when I stop at lights

[drick37]

Hi there all,

I have a 2002 Ford Explorer, 4.0 ltr, 112,000 miles. I recently did a tune up, plugs and wires, no issues, just past the 100k mile mark. Since then, when I stop at a light the idle goes way down. I changed the fuel filter and air filter. I'm hunting for a vacuum leak now. Any thoughts as to what this might be. Your insight would be greatly appreciated.

[danielsatur]

1) Clean Massive Air Flow(MAF) sensor with CRC MAF sensor cleaner.
2) Clean throttle body and IACT.
3) New upstream H02 sensors.

[shorod]

So did this idle concern begin immediately after changing the spark plugs and wires? If so, I'd start there. Make sure all connections at each end of the spark plug wires are solid. Along the path of each plug wire check for nearby vacuum lines and inspect them for cracks or breaks. Does the engine idle rough, or just low?

What type of spark plug did you put in? Some vehicles are quite particular on the spark plug style, and if you "upgrade" with a different style of plug they won't run as well.

-Rod

[drick37]

Cleaned everything, will replace the upstream O2 sensor this week before I go on a 12 hour drive. Hopefully that will do the trick as this is my driver.

[drick37]

Put motorcraft plugs in. The problem started after I put a new battery in last week. Cleaned everything that I could. Will replace the O2 sensors this week.

[danielsatur]

Save 50% by only replacing the upstream HO2 sensors, not the down stream.

The upstream O2 sensors are used by the ECU for the Air/fuel mix.
The downstream O2 sensors tells the ECU, that your cat's are working.

[shorod]

You might want to check the battery connections to make sure they are tight, then measure the voltage on the battery cables (not the battery terminals) when the starter motor is cranking over the engine as well as when the engine is idling. It is possible you installed a weak battery. Modern vehicles can do some pretty strange things when the charging system and battery is not in top shape.

For example, my wife used to have a 2002 Lincoln LS with the V6. It had a slight "misfire" at idle and would sometimes die at the end of the driveway when shifting from reverse to drive. From reading on the LS forum I learned that it was pretty common for the PCV elbow to crack or collapse and cause driveability issues. The PCM was not reporting any misfire codes (including in the PIDs) so I pulled the intake manifolds and replaced the PCV elbow (didn't see anything of concern with the original one) along with the spark plugs. Put it all back together and the symptoms were only slightly better, it still would randomly stall.

A couple weeks later I replaced the 3 year old battery and all the issues went away. Never had another stalling issue or rough idle for the next 2 years when we traded the car in.

-Rod

[danielsatur]

Lets do a smoke test on this truck!
1) Remove Air filter
2) Wrap filter in glad wrap, and put the air filter back in.
The idea is to block all air going into the intake.
3) Disconnect the break booster brake hose.
4) Light up a Black & Mild cigar.
5) Hit, and blow puffs of smoke through the break booster hose, and cover with thumb inbetween puffs.
6) Where ever you see smoke leaks, is unmetered air that the ECU doesn't know.
7) Focus on EGR, PCV, and Air Intake system.

This test is so much safer than using flammable fluids.
A smoke test is probably $100, and a cigar is so much cheaper!

[drick37]

Never heard of the smoke test before. I'm going to give that a try after I take my battery to Autozone for a test, they may have sold me a dang near dead "new" battery. It's happened before.

[drick37]

Okay, today, click, click, click, no start, checked all the fuses. Nothing, two suspects, the starter or the fuel pump or pressure relay. Have to go and get a code puller to diagnose further.

[shorod]

If the "click, click, click" was at a single turn of the key to Start, the multiple clicks would suggest a low voltage/current issue rather than a problem with the starter or fuel system. Check the connections for the battery to make sure they are clean and tight. Check the battery voltage without a significant load and also when trying to start the engine. Measure both on the terminals of the battery as well as on the battery cables. If there is a measurable difference between the terminals and the cables, you have dirty cables. If not but the voltage is low you may have a weak battery that cannot handle cold + load, or you may have a drain on the battery that sucked it down.

-Rod

[drick37]

A weak battery is the culprit. I checked the voltage and the connections, took the alt. out and had it bench tested. Took the battery out, had it tested, weak. Just bought it two weeks ago, taking it back today. I'll have to check for anything that may be bleeding it out after I get it installed or it just may be a bad battery. None of my problems started till I installed a new battery.

Thanks for all the help.

[shorod]

Glad to hear that your fix may be an easy one. Thank you for the follow-up!

-Rod

[danielsatur]

With the ignition off, check for a battery drain using a DVM!
A non-switched control module connected to a Batt fuse could be causing a battery drain.

Also battery cable/wire corrosion could keep the alternator from charging the battery.