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high idle while driving - Printable Version

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high idle while driving - bigbuck - 01-16-2017 07:23 PM

I have a 1995 Ford Escort wagon with a 1.9l engine with approximately 179000 miles. I'm here in Wisconsin. I recently had the head rebuilt. Before I did that I was experiencing a rough irregular idle on a cold start up but it would smooth out after 30 seconds or so. I thought it was a symptom of the leaking head gasket. I was getting a lot of goo in the PCV valve. So now that it is all back together, it sill had the idle problem. I took off the idle air control valve and it seemed to be dirty and sticky so I replaced it Now it revs real high on any start up and comes down to normal. When I drive it the idle speed comes way up to the point that I don't need to accelerate. but won't come down. I need to brake to control my speed. Then when I come to a stop, the brakes quit working. It feels like the power brakes quit and like you're sliding on ice. I also tried replacing the throttle position sensor with one I had from an old Escort of the same year and there was no change. Please help!

RE: high idle while driving - Rupe - 01-17-2017 12:55 AM

Wow, you have yourself a hand full with a 22 year old car and high miles so let's dissect these issues to see where we can go.

If you haven't done so already, at that age I would replace every vacuum line and then make sure they are all connected to the proper place... mostly because parts are cheap and the age makes then suspect, along with some recent work that may have added to something not being in the right place on reassembly. Some hoses that look ok may be soft enough to collapse after the engine warms up, especially if they were covered (inside?) with oil. The line going to the PCV should be fuel line, not vac line just for this reason. I have also seen the vac line to the brake booster do the same thing. That one had me scratching my head on a job even with 40 years in the business. I had to catch it in the act before it made sense.

That all said, we need to nail down this high idle situation so let's look at the obvious without leaving the driveway. Does the idle creep back up on it's own as the engine warms up? Will it go down again if you push on the throttle linkage? Have you cleaned out any of the passages around the throttle plate and IAC (Idle Air Control) since replacing it? Ya know, that old sludge could still be lurking and gumming things up. If pushing on the throttle linkage helps, is there an issue with the throttle cable or gas pedal sticking? Get a can of GOOD carb cleaner and go over all of it. (my personal favorite is Cyclo brand in the red / white can) The better stuff is well worth the extra $3 because it WILL do the job.

My gut feeling is the high idle along with possible soft vac lines is going to solve most of the problems concerning the brakes.

While I have your attention, you should also clear the engine computer of codes. On this older vehicle it can be done by disconnecting the battery for 10 minutes. If the check-engine light comes back on later at least you know any codes in storage will be for a new problem, not something lingering from all of your testing and poking at stuff.

Let us know how you make out and we can chat more as you move forward.

RE: high idle while driving - Garner - 01-17-2017 06:54 AM

A note to go with what Rupe said about the gas pedal sticking. I'm thinking that Wisconsin would be cold and snowy now? I had a guy here in PA that would get in his truck with snow covering his boots. The heater would melt the snow right onto the gas and brake pedals. He complained of similar issues that you are having. We found so much ice built up around the pedals that they were sticking down. We preyed the floor mats out, thawed, and dried them, chipped the rest of the ice out around the pedals, put the mats back in, and all was good. It's worth a look if it is cold there in Wisconsin. Please keep us informed as to what you find.

RE: high idle while driving - bigbuck - 01-17-2017 10:13 AM

Thanks for the quick response. I also thought about the EGR system. From what I have read, that could also case some idle problems. Your thoughts? It is also my understanding that there is a check valve in the brake vacuum line, actually in the line on this car. Would that cause the braking condition I am experiencing? Could I run it without the check valve?

RE: high idle while driving - Rupe - 01-17-2017 11:21 AM

EGR leaks will not cause a fast idle. If anything that would make for a rough idle / stall condition.

The check valve for the brake booster is usually the small fitting where the hose connects right on the body of the booster. It's job is to hold the vac so when you mash the gas the vac doesn't go away. In all my years I have never seen one that went bad internally but I have seen them crack or break externally. As I mentioned before, I have seen the brake vac hose get soft and collapse after the engine warms up but that's also a fluke. The only time I saw it was NOT on an older car so I suspect a manufacturing / design defect.

Back to what can cause your condition: I suspect either the booster vac is going away or the idle is sticking high enough that the engine is over-powering the normal brake operation.

BTW, a 3rd suspect, although rare, is the booster diaphragm could be leaking and causing extra air into the engine, which in turn raises the idle AND causes loss of brake boost. Normally you would expect to hear a sucking noise under the dash where the brake rod comes through. (noise changes with brake application) You can isolate this via plugging off the vac hose for the booster. When I say it's rare, I have only changed maybe 3 boosters for this issue in the last 45 years.

Keep us posted!

RE: high idle while driving - bigbuck - 01-22-2017 10:46 AM

First of all I want to thank you both for your input in helping me solve my problem. Your technical advice not only directly helps with the problem, but while going through the process, I learn more and more about how the systems work. The first thing I did was make sure the throttle was moving freely. That seemed to be good. Then I raced all the vacuum lines I could find and replaced anything that looked remotely sketchy. I plugged the vacuum port for the speed control to eliminate it. I don't use cruise control anyway and there is a lot of vacuum line in that system to evaluate. After each correction, I tested it and still had the runaway idle condition. I took the old idle air control valve, cleaned it up a little better and reinstalled it. The idle problem went away! I've driven the car now for a few days in various conditions and have not had the problem return. I guess the part was defective. I may have to replace it in the future, but for now, things are working good. Thanks again for your help!

RE: high idle while driving - Rupe - 01-22-2017 11:37 AM

Thanks for the follow up with the "final fix" as most people don't bother. This may help others reading here in the future.

RE: high idle while driving - Garner - 01-23-2017 07:17 AM

I also want to thank you for the Follow Up! I appreciate hearing the "Fix" to the problem.