# Engine starts and idles fine, stumbles when acclerator is pressed quickly **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** mercury, capri\ **Created:** [July 2, 2024, 1:25am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266 "2024-07-02T01:25:44Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![km4hr\_147946](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@km4hr\_147946](https://community.cartalk.com/u/km4hr_147946)\ **Post date:** [July 2, 2024, 1:25am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/1 "2024-07-02T01:25:44Z")
1992 Mercury XR2 (Mazda 323 drivetrain). Engine starts and idles perfectly. Stumbles and sputters when accelerator is pressed quickly and won’t rev up. When accelerator is pressed very slowly engine revs up properly. Was running perfectly yesterday. What went wrong? ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 2, 2024, 1:39am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/2 "2024-07-02T01:39:35Z")
Check the resistance of the throttle position sensor while operating the throttle by hand. If the resistance jumps all over the place while doing so, the TPS needs replacing. > **[Mercury Capri Throttle Position Sensor / Capri Throttle Position Sensor /...](https://shop.moderncapriparts.biz/catalog/ProductDisplay.cfm?id=188326&cid=148)** > > WOW .... Although LONG DISCONTINUED from Ford for CLOSE TO A DECADE, we have a very limited supply of BRAND NEW ("NOS"), ORIGINAL, (Ford/ MOTORCRAFT) Mercury Capri Throttle Position Sensors / Capri Throttle Position Sensors, Mercury Capri... Tester ---
**Author:** ![shanonia](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@shanonia](https://community.cartalk.com/u/shanonia)\ **Post date:** [July 2, 2024, 2:14am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/3 "2024-07-02T02:14:58Z")
If you find uneven change in resistance, as Tester explained, you can first try electronics parts cleaner spray in the TPS. It worked for me and I avoided having to replace the TPS. ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [July 2, 2024, 3:35am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/4 "2024-07-02T03:35:34Z")
You might also clean out your idle air control valve (IACV). Even if it’s not a problem - it’s pretty easy and it never hurts to clean stuff! ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 2, 2024, 4:02am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/5 "2024-07-02T04:02:41Z")
> [@cigroller](#): > > You might also clean out your idle air control valve (IACV) The IAC valve is out of play once the accelerator is depressed. Tester ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [July 2, 2024, 4:11am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/6 "2024-07-02T04:11:22Z")
Yes. It’s supposed to be. But if it’s sticky, then it can … well, be sticky. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 2, 2024, 4:36am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/7 "2024-07-02T04:36:20Z")
Whatever the hell you typed? Tester ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [July 2, 2024, 5:27am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/8 "2024-07-02T05:27:21Z")
[![](https://global.discourse-cdn.com/cartalk/original/3X/9/1/91817f0574da7d944400c52ff96b9f8e9d380940.jpeg "Father, forgive me, I am a worm 🤘 #highlander #lambert #connery #brown #macleod #ramirez #kurgan") ](https://www.youtube.com/watch?v=rKnu4TO7qzs) Say what you want. I’ve had a sticky/sluggish IACV cause acceleration stumbles. I just gave a cheap and easy maintenance item that wouldn’t hurt > [@cigroller](#): > > Even if it’s not a problem Lighten up King mechanic. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [July 2, 2024, 5:36am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/9 "2024-07-02T05:36:48Z")
> [@km4hr\_147946](#): > > When accelerator is pressed very slowly engine revs up properly. Is the car drivable when accelerating slowly? Or is this while in park/neutral? The fuel pump might be weak, measure the fuel pressure while accelerating. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [July 2, 2024, 5:45am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/10 "2024-07-02T05:45:15Z")
Possible MAF, unplug it and see if it helps any with acceleration, the MAF sensor can make older cars act all kinds of strange sometimes… ---
**Author:** ![glasspilot](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/glasspilot/32/27886_2.png) [@glasspilot](https://community.cartalk.com/u/glasspilot)\ **Post date:** [July 2, 2024, 4:44pm UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/11 "2024-07-02T16:44:23Z")
Well, it’s a 1992 car. Does it have a carburetor? If so, the accelerator pump might need tweaking. That was the cause of hesitation back in the carb days. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [July 2, 2024, 5:22pm UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/12 "2024-07-02T17:22:52Z")
> [@glasspilot](#): > > Does it have a carburetor? Throttle body ---
**Author:** ![km4hr\_147946](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@km4hr\_147946](https://community.cartalk.com/u/km4hr_147946)\ **Post date:** [July 2, 2024, 5:48pm UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/13 "2024-07-02T17:48:18Z")
Thanks! Sounds reasonable. I’ll see if I can do that. It’s been over 100 degress here for the past few days and I don’t have a shop. Think I’ll drive my other car until it cools down a bit. ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [July 2, 2024, 5:54pm UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/14 "2024-07-02T17:54:41Z")
> [@Nevada\_545](#): > > The fuel pump might be weak, measure the fuel pressure while accelerating. Yes another possibility. Pressing down slowly allows the oxygen sensor to correct for the lean condition. ---
**Author:** ![km4hr\_147946](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@km4hr\_147946](https://community.cartalk.com/u/km4hr_147946)\ **Post date:** [July 2, 2024, 5:54pm UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/15 "2024-07-02T17:54:48Z")
It acts exactly like a accelerator pump problem. But it has port fuel injection, one injector located in each intake manifold leg where the manifold bolts onto the cylinder head. ---
**Author:** ![km4hr\_147946](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@km4hr\_147946](https://community.cartalk.com/u/km4hr_147946)\ **Post date:** [July 2, 2024, 8:21pm UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/16 "2024-07-02T20:21:37Z")
Wouldn’t you know it? I started the engine today and it runs perfectly, at least in my yard. I’m afraid to take it out on the road. Maybe I’ll try it early tomorrow morning when I’ll have plenty of time to tow it home if necessary. We had a storm the night before the problem occured. The car leaks a little water into the passenger compartment. Maybe the computer got wet. I don’t even know where the computer is. But this car has been out in the rain for years with no problems. Thanks to all of you for your thoughts and recommendations. I’ll report back if there’s any news. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [July 2, 2024, 11:13pm UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/17 "2024-07-02T23:13:07Z")
A simple vacuum leak could cause that symptom as well. Do you notice any split or disconnected vacuum hoses in the engine compartment? If your car uses vacuum actuators for the hvac, another common source for a vacuum leak. This may or may not turn the check engine light on. Is it on? A problematic EGR system is something else to consider. ---
**Author:** ![km4hr\_147946](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@km4hr\_147946](https://community.cartalk.com/u/km4hr_147946)\ **Post date:** [July 3, 2024, 2:26am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/18 "2024-07-03T02:26:42Z")
The vacuum hoses show signs of age but none that I’ve seen are broken. I don’t hear any hissing sounds like a vacuum leak. I’ve wondered about the check engine light. I don’t recall ever having seen one. If there is one it’s not on now, or maybe the bulb is burned out. I also wonder if there’s a diagnostic connector and if a reader can be plugged in to check for trouble codes. Unfortunately I don’t have a shop manual. I need to investigate this further because I seem to recall that the car has a standard Ford engine control computer. If that’s true it should have a check engine light that can be used to blink trouble code numbers. I’ll have to check into that. Thanks for reminding me. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 3, 2024, 2:36am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/19 "2024-07-03T02:36:23Z")
> [@km4hr\_147946](#): > > I also wonder if there’s a diagnostic connector and if a reader can be plugged in to check for trouble codes. This provides instructions how to retrieve the OBDI codes from your ford, and their definitions. > **[How to Retrieve Ford OBD1 Codes and Definitions](https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval)** > > Repair guides, articles and advice for car owners, enthusiasts and repair technicians. Tester ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [July 3, 2024, 3:45am UTC](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266/20 "2024-07-03T03:45:19Z")
That brings back a lot of memories… [Next page](https://community.cartalk.com/t/engine-starts-and-idles-fine-stumbles-when-acclerator-is-pressed-quickly/195266.md?page=2)