Posted on 09/18/2025 4:59:38 PM PDT by EinNYC
My 2006 Scion Xa (with only 74,000 miles on odometer) has lately been "jumping" when I first start it up for the first time in a day. I had my local mechanic put it on the scope, but he found nothing. He changed 3 of the ignition coils. No change. He changed a small hose from the ignition complex, which was hard and frayed at the ends. It's a little better, but still jumps when you first start it up. The mechanic drove it around, and it didn't miss. It ONLY does that when you first start it up, first time in the day. After a couple of minutes, it drives fine. Any idea what else could be the problem? I love my Scion and this is the first problem it's ever presented in all those years.
The coils, but what about the plugs?
Maybe it’s a fuel issue?
Have him change the fuel filter.
Also, how long has your current tank of gas been in the car? Gas can go bad... this is sometimes a problem in cars that aren’t driven a lot.
How high does it jump?
(sorry, don’t associate that term with a car unless it’s a low rider)
Aren’t you a Scion expert?
You need to clean your valves. You can get a valve clear kit from advanced auto parts for $20. Easy to do. Just look up a YouTube video on it.
Dirty fuel injectors.
Maybe crap in gas tank.
Or poor quality gas.
At least that’s my guess.
Valve cleaner kit….SeaFoam kit
Plugs, wires, cap, and sensors. Once engine heat dries out the condensation things settle down if it’s those things.
“Jumping” sounds like dieseling. Fuel in cylinders igniting not in proper sequence.
But you say it happens only at morning start-up.
Dont think it would be plugs. How would it get ok and run right the rest of the day?
Has to be fuel. Would the fuel pump not shut off properly? Would it flood the pipe from the fuel tank, so that at startup, there’s excess fuel to do the dieseling?
Never been a mechanic... I just handed tools to my dad.
It does sound like a fuel issue. A bottle of HEAT will at least get any water out of there. Changing the fuel filter wouldn’t hurt, car is almost 20 years old. Those are some cheap trouble shooting options anyway.
I have the same problem with my wife.
I’m agreeing with OKSoonee that it could be a fuel issue. Have your mechanic check to make sure the injectors are working properly, and check the fuel pressure to make sure the fuel pump is working properly.
I had a bad fuel pump in one of my cars do something similar. Not exactly the same, but it was almost like a bad miss when it wasn’t working properly. It was intermittent as well — sometimes bad, other times fine.
“Ain’t got no gas in it…mmm hmm…”
Oldeconomybuyer wins the Internet for today!
I use up about 3/4 of a tank of fuel per week or within 2 weeks. I get my gas at Costco, because they are cheaper than station and why not? So I don’t have a tank of old gas hanging around for a month or so. Once the misfiring of the first couple of minutes is over, the car runs well. Now it occasionally misses once while driving, which I wonder if connected to replacement of that little hose.
You need to get new jumper cables.
Not high enough to jump rope with the little girls next door.
Based on the symptoms you described—a "jumping" sensation (likely rough idle or misfire) only on the first cold start of the day, which improves after a couple of minutes and doesn't recur while driving—here are some common culprits for a 2006 Scion xA (which shares its 1NZ-FE engine with models like the Toyota Echo/Yaris). These build on what your mechanic has already tried (ignition coils and a potentially frayed vacuum or PCV hose). Since no codes showed up on the scan and the issue is cold-start specific, it's often related to temperature-sensitive components, accumulated moisture, or air/fuel mixture imbalances that resolve as the engine warms. I'll prioritize likely causes and suggest next steps.
1. Remaining Ignition System Issues
- Spark Plugs: If they haven't been replaced recently (especially with only 74k miles, but age matters more than mileage), worn or fouled plugs could cause a cold misfire that clears up once warm. Moisture buildup overnight in the plug wells or connectors can exacerbate this, leading to initial shaking.
- The Fourth Ignition Coil: Your mechanic replaced three, but these engines have four coil-on-plug units. A weak or failing remaining coil might only show issues on cold starts due to higher resistance when cold.
- Next Steps: Inspect and replace all spark plugs (use OEM or NGK/Denso equivalents). Test the last coil's resistance (should be around 0.4-0.6 ohms primary, 7-11k ohms secondary). If moisture is suspected, apply dielectric grease to the coil boots and plug connectors.
2. Vacuum Leaks (Building on the Hose Replacement)
- The frayed hose your mechanic fixed was likely a vacuum line (possibly from the intake manifold or PCV system), and since it helped "a little," there could be additional small leaks that are more pronounced when the engine is cold (rubber seals contract). Common spots: intake manifold gasket, throttle body gasket, or other brittle hoses that harden with age.
- Next Steps: Perform a smoke test (safer than spray methods) to detect hidden leaks. Inspect all vacuum lines, including the PCV valve and hose—if the PCV is clogged or sticking, it can cause rich/rough conditions on startup. Replace the PCV valve (cheap, around $10-20) as preventive maintenance.
3. Dirty or Faulty Sensors Affecting Air/Fuel Mixture
- Mass Air Flow (MAF) Sensor: Dirt or carbon buildup can send incorrect readings to the ECU, causing a lean or rich mixture on cold starts. This is a top cause for rough idle in these models and often doesn't throw a code until severe.
- Engine Coolant Temperature (ECT) Sensor: If faulty, it might tell the ECU the engine is warmer than it is, leading to insufficient fuel enrichment on cold starts and initial jumping.
- Intake Air Temperature (IAT) Sensor: Similar issue—could misreport cold air temps, disrupting the mixture.
- Next Steps: Clean the MAF with dedicated MAF cleaner (not carb cleaner, as it can damage it). Use a scan tool with live data to monitor ECT and IAT readings on a cold start (ECT should start near ambient temp and rise steadily). Replace if readings are off.
4. Fuel System Problems
- Dirty or Leaking Fuel Injectors: Over time, injectors can get gummed up or drip fuel overnight, flooding the cylinders and causing a rough cold start that burns off quickly.
- Fuel Pressure Issues: A weak fuel pump or regulator might not hold pressure after sitting, leading to initial starvation or inconsistency.
- Next Steps: Add a fuel system cleaner (like Sea Foam or Techron) to a full tank and drive it. If that doesn't help, have the injectors tested for leaks (ultrasonic cleaning or replacement if needed). Check fuel pressure with a gauge—should hold around 44-50 psi when primed.
5. Throttle Body or Idle Air Control (IAC) Valve
- Carbon buildup in the throttle body or a sticking IAC can cause unstable idle, especially cold when the engine relies on the IAC for extra air. Your low mileage suggests less wear, but 19 years of age can still lead to gunk.
- Next Steps: Remove and clean the throttle body and IAC with throttle body cleaner. Relearn the idle by disconnecting the battery for 10-15 minutes after cleaning (or use a scan tool).
General Advice
- Diagnosis Tips: Since it only happens on the first start, leave the car at the shop overnight so they can replicate it cold. Ask for a live data scan during the issue (monitor RPM, fuel trims, and misfire counts). No codes doesn't rule out intermittent problems—tools like an OBD-II scanner with graphing can catch brief glitches.
- Why It Improves Quickly: Cold starts stress components more (thicker oil, contracted parts, moisture), but as heat builds, mixtures normalize and issues mask themselves.
- If DIY isn't your thing, a Toyota dealer might have more model-specific experience (Scion was a Toyota brand). Total fix costs could range from $50 (cleaning/DIY parts) to $300+ (coils/injectors), depending on the root cause.
If you provide more details (like exact "jumping" feel, any smells/smoke, or recent maintenance), I can narrow it further.
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