Skipping and rough idle

[Slappy]

1998 Explorer - Stock

I hesitated to post this because I know there is a myriad of issue that can cause this. I’m in a fanatical bind and all shops I have visited want $135/hr just to diagnose the problem. This issue occurred last year around this time and a young man where I have my oil changed found that a vacuum hose was unattached. He simply reattached it/problem solved. It’s happened again and I don’t see any unattached vacuum hoses.

Symptoms: Run perfect until the engine reaches normal running temperature then it skips and idles roughly. It’s exactly symptoms i find on the internet for a loose or unattached vacuum hose. But I can’t find the hose. Is there a typical place to look? It never actually stalls but there is a power loss.

Any ideas?

Thanks

Bob

 

[J_C]

Welcome to the forum!

I'd hook up a scan tool capable of Ford specific codes (and pull any codes) and live data and look at the long term fuel trim, if going very positive then yes it seems like a vac leak, or low fuel pressure, or dirty MAF sensor, or bad temp sensor. Also note any other live data that looks wrong, particularly when running rough.

If all else fails, do a smoke test to find a vac leak. Simplest /cheapest setup I know to do that, is get a $1 pack of cigars at the gas station and a hand pump like this, also available on amazon and elsewhere under different brands:

Multi-Use Transfer Pump

Amazing deals on this Multi-Use Transfer Pump at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

There are youtube videos showing usage examples.

https://www.youtube.com/results?search_query=hand%20pump%20smoke%20test

Seal up the intake snorkel after the air filter box (plastic bag over it with a big rubber band or whatever), and then one of the popular places to put the smoke in is the brake booster hose, unless of course it's your brake booster itself that's leaking.

If it's not a hose then another common leak is the intake manifold gasket(s).

Another alternative is to pull the vac lines off the intake manifold one at a time and block the port they plug onto, or pinch them shut with a pair of pliers, to see if the (potential) lean condition goes away. I hate doing that on vac lines this old because they may be permanently stretched or brittle, and crack or break if you disturb them, so you could end up with more vac leaks than you started with.

 

[wollimann]

1998 Explorer - Stock

VIN X or E 4.0
Vin P 5.0

 

[410Fortune]

98 explorer came w three engine options

Which engine do you have