1990 Ford F-150 Requires Some Old Fashioned Troubleshooting to Fix

This 1990 Ford F-150 was suffering from idle issues that couldn’t be diagnosed using a scan tool.

For quite a few years now, troubleshooting problems in modern vehicles has been rather easy, thanks to technology. Generally, one can just plug up a diagnostic tool or even a laptop and immediately figure out what’s wrong, which is quite different from the old days, when it took more mechanical know-how and a bit of hunting to find a problem. However, YouTuber the Car Wizard, or David Long as he’s otherwise known, recently had to turn back the clock to figure out what was causing idle issues with a customer’s 1990 Ford F-150.

The owner of this 1990 Ford F-150 was using the proverbial “parts cannon” method to try and fix it himself prior to bringing it into Long’s shop, replacing everything he thought might be causing the surging, high idle. Eventually, he got frustrated and decided to consult an expert, which was obviously a good idea, because as Long points out, a diagnostic tool is pretty much useless in this situation since the issues the truck is suffering from won’t typically trigger a code or check engine light.

On top of that, many of the scan tools uses to diagnose problems with vehicles of this age simply don’t exist anymore, or are difficult to find, at the very least. Thus, Long walks us through his process of tracking down the culprit, naming off four potential areas that might be to blame. He then explains each one and identifies what he found on this particular truck, which happens to have more than one problem area that’s leading to the 5.0-liter V8’s idling woes.

First, a voltmeter reveals that the MAP sensor is bad and needs to be replaced, which solves the surging idle problem. However, the engine still wasn’t running right, so Long used a smoke machine to find a very small vacuum leak, which was enough to throw things off. Finally, he also discovers that the throttle body is bad, but quickly discovers that a replacement isn’t easy to come by in today’s world ripe with parts shortages.

Regardless, the process Long follows in this diagnosis and repair is undoubtedly interesting, and proves that there’s still a need for experienced, knowledgable mechanics who don’t simply rely on electronics to diagnose problems with vehicles.

Join the Ford Truck Enthusiasts forums now!

Brett Foote

Brett Foote has been covering the automotive industry for over five years and is a longtime contributor to Internet Brands’ Auto Group sites, including Chevrolet Forum, Rennlist, and Ford Truck Enthusiasts, among other popular sites.

He has been an automotive enthusiast since the day he came into this world and rode home from the hospital in a first-gen Mustang, and he's been wrenching on them nearly as long.

In addition to his expertise writing about cars, trucks, motorcycles, and every other type of automobile, Brett had spent several years running parts for local auto dealerships.

You can follow along with his builds and various automotive shenanigans on Instagram: @bfoote.