Naw, it's a straight Gerbil Drive. See?
Posted on 09/18/2025 4:59:38 PM PDT by EinNYC
If you can describe the “jumping” (e.g., shaking, stuttering, or RPM fluctuations) or check for dashboard lights during the issue, I can refine this further. Let me know if you want me to search for Scion xA-specific forums or posts for similar cases.
1. Ignition System (Moisture or Contamination in Plugs/Coils)
- Forums frequently cite moisture in spark plug wells/connectors causing cold misfires that vanish as heat evaporates it—exacerbated by age (your 19-year-old car) even at low miles. Oil leaks into plug tubes from a degraded valve cover gasket can foul plugs/coils similarly.
- Your partial coil replacement (3 of 4) aligns with reports of non-OEM or mismatched coils failing cold; one xA owner swapped the suspect coil under warranty and fixed it.
- Next Steps: Pull plugs to check for oil/moisture (clean wells, apply dielectric grease). Replace all plugs if not recent ($20-40). Inspect valve cover gasket for leaks ($50-100 to replace). Test/swap the fourth coil ($30-60). A ScionLife user fixed a similar jerking cold start this way.
2. Throttle Body or Idle Air Control (IAC/ISCV) Buildup
- Carbon/gunk in the throttle body or IAC causes unstable cold idle (low/high RPM swings or shaking), as the engine struggles for air balance before warming. This resolved hesitation/roughness in multiple high-mileage xA/xB cases after cleaning.
- Next Steps: Clean throttle body and IAC with dedicated cleaner ($10-20, DIY in 30-60 min). Reset idle by battery disconnect (10-15 min) or scan tool. One 189k-mile xA owner reported full fix from this alone.
3. Mass Air Flow (MAF) Sensor or Vacuum Leaks
- Dirty MAF misreads cold air/fuel, leading to lean/rich mixtures on startup—common in 1NZ-FE engines, often no codes initially. Builds on your hose fix; forums suggest checking manifold gasket too.
- Next Steps: Clean MAF with MAF spray ($10). Smoke test for leaks ($50-100). xB owners (same engine) saw big improvements cleaning MAF/throttle.
4. Engine Coolant Temperature (ECT) Sensor
- Faulty ECT under-reports cold temps, starving fuel enrichment and causing jumping that eases as it warms. Mentioned in hesitation threads, though less common.
- Next Steps: Scan live ECT data on cold start (should match ambient, rise steadily). Replace if off ($20-50).
5. Fuel System (Lower Priority Post-Additive)
- Rare in forums for cold-only issues, but one suggested bad gas or clogged cat (from chronic misfires) causing backpressure. Your additive flop rules out minor injector gunk.
- Next Steps: Pressure test ($50). Inspect cat if shaking persists (but unlikely without smoke).
Forum Diagnosis Tips
- Replicate cold: Overnight at shop for live scan (RPM/fuel trims/misfires). No codes? Graphing OBD tool catches intermittents.
- Toyota/Scion dealer for 1NZ expertise; low-mile cars like yours often just need maintenance catches (e.g., 5k-mile xA rough idle was moisture).
- Costs: $50-150 DIY cleans/grease; $200-400 shop (gasket/coils). Threads emphasize these engines' durability—many hit 200k+ with basics.
Exact "jumping" details (e.g., RPM drop? Acceleration stutter?) could pinpoint more. Want me to browse a specific thread deeper or search Toyota Echo equivalents?
You mean like Up and Down? How high and now fast? Like how many times a minute does it jump? Is it like a regular rhythm or just kinda random like.
Does it jump side to side any at all? How about forward and backwards?
Does it wiggle any? If it did that would be really bad.
Is that one of those cars that the Hamsters drive?
That could be your problem right there. Hamsters may have taken control over your car.
Why should I need new jumper cables? I have a next door neighbor with a brand new charger box that starts cars without a charging cable.
Can you let the mechanic keep it overnight and start it up himself first thing, with it hooked up to diagnostic?
Sounds like moisture is getting into the cylinders. Get a pressure test on the Cooling system and a blow down leak test.
Why should I need new jumper cables? I have a next door neighbor with a brand new charger box that starts cars without a charging cable.
That's funny, my My 2006 Scion tC has only 17,000+ miles. No wonder your car is champing at the bit.
But seriously I suspect it is the Emissions/smog devices.
This happened to me:
Scion 02/15/2025 Diagnostic trouble code (DTC) P0456 stands for “Evaporative Emission System (EVAP) Small Leak Detected.” Your car’s computer will trigger this code when it thinks that there’s a minor leak somewhere in the evaporative emissions control (EVAP) system. Common causes of a P0456 code are faulty EVAP hoses, a leaking charcoal canister, or a damaged gas cap. A vehicle with a logged P0456 code can show symptoms like an illuminated check engine light and increased hydrocarbon emissions from the leak point.This turned out to be the gas cap was put back correctly and I figured out someone had stolen gas from the tank.
I had already purchased an Innova Car Scan Advisor 5210 to read the automobile codes that indicate possible problems in the computer control system.
That's exactly what I've done, twice, to try and find an answer to this.
With so few miles after nearly 20 years I second clogged injectors and old fuel. You try additives but if they don’t help have them professionally cleaned at a mechanic. They may even need replaced.
My gas cap screws on securely. So that’s not it.
Naw, it's a straight Gerbil Drive. See?
The nature of the jumping is that the car feels like it’s jumping. And occasionally feels like it’s gonna stall, but doesn’t.
Have you considered a clogged catalytic converter?
It sounds like a fuel system issue to me. I use a product called Startron, it comes in a bright blue plastic bottle. If Autozone or O’reillys doesn’t have it Ace Hardware or Tractor Supply Company usually does. It encapsulates the ethanol in the gasoline and cleans the crap out of the fuel system. I use it in my cars that don’t get driven regularly. I have been using it for years and have no problems with fuel contamination. The ethanol causes problems in fuel systems, even with newer cars. I use it in lawn mowers and other power equipment as well.
^ this
...also borescopes (preferably articulating) are pretty cheap these days.
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